Pandoc: Permit adding attributes to all Markdown elements

[phyllisstein]

I'd like to suggest that Pandoc allow attributes to be attached to any Markdown element, not just code blocks. So for example, if it encountered this:

#{.main} Header

it would generate this:

<h1 class="main" id="header">Header</h1>

rather than this:

<h1 id="main-header">{.main} Header</h1>

Ditto for, say:

----{.main}

...which is probably even legible enough to fit with Markdown's philosophical aversion to looking, well, marked-up.

[jamiefolson]

FYI conversations on this topic date back 5 years:

• discussing maruku's attributes
  
  
  
  • discussing implementation issues without expanding the syntax
  
  
  • this long but well-thought-out request for new syntax
  
  

I for one think it's surprising that nothing seems to have been done to facilitate this. I understand the desire not to pollute the syntax, but it seems like people are taking extraordinary measures to work around this limitation.

[jgm]

Would you count 1.11's allowing attributes to be added to headers
as progress?

[phyllisstein]

John,
I thought that was a terrific step, along with the inline_code_attributes extension. I'm looking forward to when classes and key/value pairs are implemented for headers, since the particular use case I had in mind involved setting an identifier and an onClick event.

Thanks so much for all your work on Pandoc; it's really a thing of beauty.

[jgm]

+++ Daniel Shannon [Mar 15 13 18:04 ]:

John,
I thought that was a terrific step, along with the
inline_code_attributes extension. I'm looking forward to when classes
and key/value pairs are implemented for headers, since the particular
use case I had in mind involved setting an identifier and an onClick
event.

They are already implemented in 1.11!

% pandoc
# Hi {#foo .bar .baz key=val}
^D
<h1 id="foo" class="bar baz" key="val">Hi</h1>

[jamiefolson]

I think attributes for headers are a great and wonderful thing. I also think that there are totally valid reasons for wanting to add attributes to arbitrary elements. For example, in the reports package for R, the author, possibly intimidated by haskell, resorted to a series of fragile regular expressions to try add the necessary classes and attributes to html output.

Certainly, the "fragment" class for reveal.js could and probably should be set by a new output format for pandoc, however, it's a lot harder to come up with a solution for the transition options. Both Beamer and reveal.js allow the user to configure how and when transitions occur (I don't know about all the other js templates).

Custom attributes would make it simple for reveal.js and even for beamer, the necessary script would not be complicated. Conceptually, such concepts as how and when to reveal an element _feel like options_ rather than some new syntactic element. Alternative solutions would seem to require awkward detection and parsing of (to pandoc) literal string elements.

[luc-j-bourhis]

Imho tables are in dire need of that new syntax for attributes. It is not rare to need different tables to be displayed with different styles.

[thriveth]

And there are different LaTeX figure-environments. Allowing to set custom attributes to an image tag would mean one could more easily distinguish different kinds of figure. Other writers could simply ignore it.

[jgm]

@jamiefolson: pandoc now includes a uniform syntax for transitions, which gets output as \pause in beamer and using fragment divs in revealjs. Of course, you can also just use a <div class="fragment"> in the markdown source, but this won't be portable if you decide to switch to beamer.

@luc-j-bourhis, @thriveth: You can wrap a table or figure with a div that has attributes. Are there reasons the attributes have to be on the table or image itself?

[thriveth]

@jgm I wasn't aware of that, but looking at #1242 I can see it is possible, but also witht he caveats that @blaenk mentions there.
I understand that it would be very work heavy and difficult to implement without ambiguities and messy syntax, so I second @blaenk's suggestion to implement an attribute field to the image element (because I find I almost always need to add some kind of metadata/attribute to it) and leave the rest to div/span solutions.

[mb21]

With image attributes underway, I could take a look at adding attributes to a few more elements if this is desired:

• Link #170
• Table #813
• BlockQuote (see example in #1242)

While the HTML writers would pass through all attributes, the others would just support the id and classes where appropriate. So beyond referencing tables and blockquotes, it would primarily enable simpler filters.

The exact markdown syntax for tables and blockquotes isn't exactly obvious, but I tend to favour the variant where the attributes have to be on their own line, trailing the actual table or blockquote (see the commonmark discussion and proposal).

[thriveth]

This is really great news!
Probably means I will soon be able to write journal article fully in
Pandoc Markdown without or almost without manual editing in LaTeX.

On 12/30/2014 01:42 PM, mb21 wrote:

With image attributes underway
https://github.com/jgm/pandoc/pull/1806, I could take a look at
adding attributes to a few more elements if this is desired:

• |Link| #170 https://github.com/jgm/pandoc/issues/170
• |Table| #813 https://github.com/jgm/pandoc/issues/813
• |BlockQuote| (see example in #1242
  https://github.com/jgm/pandoc/issues/1242)

While the HTML writers would pass through all attributes, the others
would just support the |id| and |classes| where appropriate. So beyond
referencing tables and blockquotes, it would primarily enable simpler
filters.

The exact markdown syntax for tables and blockquotes isn't exactly
obvious, but I tend to favour the variant where the attributes have to
be on their own line, trailing the actual table or blockquote (see the
commonmark discussion
http://talk.commonmark.org/t/consistent-attribute-syntax/272/ and
proposal https://mb21.github.io/stmd/spec.html#extensions).

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[jamiefolson]

This would be fantastic. Even if attributes are mostly only available in
the data model for filtering that enables a large number of currently
difficult use cases.

Jamie Olson

On Tue, Dec 30, 2014 at 8:59 AM, Thøger Rivera-Thorsen <
[email protected]> wrote:

This is really great news!
Probably means I will soon be able to write journal article fully in
Pandoc Markdown without or almost without manual editing in LaTeX.

On 12/30/2014 01:42 PM, mb21 wrote:

With image attributes underway
https://github.com/jgm/pandoc/pull/1806, I could take a look at
adding attributes to a few more elements if this is desired:

• |Link| #170 https://github.com/jgm/pandoc/issues/170
• |Table| #813 https://github.com/jgm/pandoc/issues/813
• |BlockQuote| (see example in #1242
  https://github.com/jgm/pandoc/issues/1242)

While the HTML writers would pass through all attributes, the others
would just support the |id| and |classes| where appropriate. So beyond
referencing tables and blockquotes, it would primarily enable simpler
filters.

The exact markdown syntax for tables and blockquotes isn't exactly
obvious, but I tend to favour the variant where the attributes have to
be on their own line, trailing the actual table or blockquote (see the
commonmark discussion
http://talk.commonmark.org/t/consistent-attribute-syntax/272/ and
proposal https://mb21.github.io/stmd/spec.html#extensions).

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[stroobandt]

This issue is also listed as item 2 on this list. (Disclaimer: I have no relation to that web site.)

[fmatheus]

Would be great if any _header_attributes_ was supported in _beamer_ output.
Looks like {.allowframebreaks} and .fragile by test made in 1.15.0.6.
But why not support arbitrary attributes? In particular _c_, _noframenumbering_ and _plain_.

[jgm]

+++ fmatheus [Oct 14 15 15:05 ]:

Would be great if any header_attributes was supported in beamer output.
Looks like {.allowframebreaks} and .fragile by test made in 1.15.0.6.
But why not support arbitrary attributes? In particular c,
noframenumbering and plain.

Sounds plausible to me. This just takes a small change in
the LaTeX writer.

[jgm]

+++ fmatheus [Oct 14 15 15:05 ]:

Would be great if any header_attributes was supported in beamer output.
Looks like {.allowframebreaks} and .fragile by test made in 1.15.0.6.
But why not support arbitrary attributes? In particular c,
noframenumbering and plain.

I've added support for all frame attributes in commit
504bf3f8e79bd502f406264e2cc2794b129a26c0

[stroobandt]

Sounds plausible to me. This just takes a small change in the LaTeX writer.

Attributes to all Markdown elements is not only useful to LaTeX and Beamer.
I personally can think of many use cases for it as XHTML classes.

[jgm]

+++ Serge Y. Stroobandt [Oct 16 15 06:24 ]:

Sounds plausible to me. This just takes a small change in the LaTeX
writer.
Attributes to all Markdown elements is not only useful to LaTeX and
Beamer.
I personally can think of many use cases for it as XHTML classes.

Sure. I was responding to the (misplaced) previous comment which just
concerned Beamer attributes on headers, not to this general issue.

[jmuheim]

@jgm:

% pandoc
# Hi {#foo .bar .baz key=val}
^D
<h1 id="foo" class="bar baz" key="val">Hi</h1>

How can an ID be applied to a link? The following doesn't work:

[Als DOCX downloaden](somewhere.html) {#download_as_docx}

[jgm]

You need the very latest dev version of pandoc to apply an
ID to a link (compile from source). And you can't have a
space before the {.

+++ Joshua Muheim [Nov 25 15 14:38 ]:

[1]@jgm:
% pandoc

Hi {#foo .bar .baz key=val}

^D

Hi

How can an ID be applied to a link? The following doesn't work:
Als DOCX downloaden {#download_as_docx}

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References

1. https://github.com/jgm
2. https://github.com/jgm/pandoc/issues/684#issuecomment-159747313

[ousia]

@jgm, will all elements have attributes in Markdown?

[jmuheim]

@jgm, which version is this? I have 1.15.2.1, which came with homebrew.

[ousia]

It comes in version 1.16.x. Latest released version is 1.16.0.2.

[elotroalex]

Any updates on this? We're trying to create a workflow that will produce a web version and a print version from the same markdown file. We're using Jekyll for web deployment. Jekyll usually plays nice with kramdown, but @mfenner has been working on a gem called jekyll-pandoc. We've been knocking our heads silly trying to decide how to handle poetry. (We're lit folks). At issue right now is the inability to handle classes at the line level so we can make the right CSS to wrap our lines nicely, etc. Kramdown handles this exceptionally well, but then we'll be giving up our workflow for pandoc | *TeX which depends on pandoc-markdown. If we can get pandoc-markdown to work well with Jekyll + poetry, we will have devised an excellent solution for a large community of editors and scholars who can now produce nice PDF's and nice websites out of the same files. We're trying at all costs to avoid to have to write filters, or divide the editing workflow into two parts. Can we get attributes at the unnumbered list line and block level, and its corollary the blockquoted unnumbered list? Or is this out with the new implementation and I missed something?

[ousia]

I think the basic issue is the following:

If Markdown is based on HTML, Markdown should have three basic attributes in all elements.

And sorry, if LaTeX cannot handle this, we should find another way of dealing with XML when using LaTeX.

[mb21]

We have now Attr (i.e. attribute support) also on Image and Link elements, as can be seen on the pandoc-types Definition.hs. To add it to further elements, we'll have to change the types and then change all the writers, which takes a lot of work and is a breaking change for filters etc. Still, I hope we'll be able to add it to more elements in the future... contributions welcome :)

[elotroalex]

Thanks, @mb21. Good to hear you're still moving on this. Contributions might be forthcoming once I find a friend who can do Haskell (or time to learn myself). I see you have this generic

| Span Attr [Inline] -- ^ Generic inline container with attributes

I can't parse haskell very well, so I apologize if this sounds dumb. What is this generic inline container?

[mb21]

It's literally the native pandoc span element (there's also a div element). Unfortunately there's no markdown syntax yet (but most probably it'll be [my text]{.myClass})—meanwhile you can write inline HTML:

echo 'some _italic_ markdown with <span class="myClass">my text</span>' | pandoc -t native

The Attr means it holds attribute and the [Inline] means a list of Inline elements. see http://learnyouahaskell.com/making-our-own-types-and-typeclasses#algebraic-data-types for an introduction into haskell data types (the whole pandoc internal document AST is such a data type).

[elotroalex]

Thanks, @mb21. This is very useful. We've decided to use some HTML tags until further notice to deal with poetry. Here's looking forward to having both this new [my text]{.myClass} syntax and the coveted attribute class for any element.

Thanks for the link to this tutorial also. It seems very complete and approachable. I got the gist of the data types right away. Perhaps it will be me or someone in my team who implements, after all.

[jgm]

You know about line blocks, right?

http://pandoc.org/README.html#line-blocks

This will give you control over line breaking and initial
indentation, without sacrificing source readability.

If you want more control, you can wrap a line block in a div
with a class, and you can wrap individual lines in a span.

[elotroalex]

Hi, @jgm. Sorry I missed you the last time you came to Columbia. @denten tells me it went really well.

So, yes, we know about the line blocks. We're juggling between those and unnumbered lists. Thanks for incorporating that syntax, btw. It is definitely useful. We were butting heads against the line wrap issue, that we could easily wrangle with the {.class} syntax, and also right now we're having some issues with ConTeXt playing nice with the line blocks. I feel we're very close to solving the ConTeXt problem, so that would only leave the line wrap problem for us. And of course, we're very aware that we can solve almost everything right now using the <div> and <span> that you provide. Our ultimate goal though is to reduce the syntax as much as possible for our editors and scholars, and achieve Gruber's dream of keeping all text relatively readable in the markdown itself.

Thanks again, for jumping in.

[elotroalex]

Hm. Maybe if I show you how I was solving this problem using kramdown/jekyll for my Ed project so the thread can get a clearer sense of the need:

- O Captain! my Captain! our fearful trip is done;
- The ship has weather’d every rack, the prize we sought is won,
- The port is near, the bells I hear, the people all exulting,
- While follow eyes the steady keel, the vessel grim and daring; 
- {:.indent-3}But O heart! heart! heart!
- {:.indent-4}O the bleeding drops of red,
- {:.indent-5}Where on the deck my Captain lies,
- {:.indent-6}Fallen cold and dead.

After it's processed by the kramdown engine this renders beautifully, and the lines wrap on smaller screens.

[jgm]

What an ugly way to write a poem! Here's how you'd do it in pandoc's Markdown:

| O Captain! my Captain! our fearful trip is done;
| The ship has weather’d every rack, the prize we sought is won,
| The port is near, the bells I hear, the people all exulting,
| While follow eyes the steady keel, the vessel grim and daring; 
|       But O heart! heart! heart!
|          O the bleeding drops of red,
|            Where on the deck my Captain lies,
|              Fallen cold and dead.

[jgm]

I see what you mean about wrapping; on small screens you want the lines to wrap with some indentation, and the above doesn't do that. Well, since you're comfortable abusing unordered lists, you could always use nested lists to get the indentation you need:

- O Captain! my Captain! our fearful trip is done;
- The ship has weather’d every rack, the prize we sought is won,
- The port is near, the bells I hear, the people all exulting,
- While follow eyes the steady keel, the vessel grim and daring; 
    - But O heart! heart! heart!
        - O the bleeding drops of red,
            - Where on the deck my Captain lies,
                - Fallen cold and dead.

With appropriate CSS, this could behave just like what you have.

Markdown is meant to be readable as it stands. Explict attributes should be used only when necessary. I think that both of the methods I've suggested give you something that's much more readable in the source. The first method has the advantage of working well in all output formats, without special CSS (though you don't get as nice behavior on small screens).

If you really want to use ugly stuff, though, you could do something like:

- <span class="indent-3">But O heart! heart! heart!</span>

and so on. A little more to write, but it will give you Markdown that works everywhere.

[elotroalex]

Ah, yes I know. It is a fantastic way of writing it in pandoc's Markdown. The only problem is having the lines wrap properly on small screens or big fonts, given that this produces a <p> tag for the stanza, with line ends being <br/>. We're working out the possibilities. Our ideal situation would be to be able to wrap these lines in line-blocks with hanging indentation using the syntax as-is, or the plan B, not as elegant, but elegant enough, {.foo} solution that you offer, as opposed to kramdown's. (which is at least better than kramdown's:

- O Captain! my Captain! our fearful trip is done;
- The ship has weather’d every rack, the prize we sought is won,
- The port is near, the bells I hear, the people all exulting,
- While follow eyes the steady keel, the vessel grim and daring; 
- But O heart! heart! heart! {.indent-3}
- O the bleeding drops of red, {.indent-4}
- Where on the deck my Captain lies, {.indent-5}
- Fallen cold and dead. {.indent-6}

[jgm]

By the way, I've long thought that we should have a dedicated block element for line blocks. (Currently there is no distinctive representation of line blocks in the AST; instead, line blocks are parsed as paragraphs with line breaks.)

This would be good for your purposes, as you could use a filter or custom renderer to customize the output. (And maybe the default renderer could have a different output than a <p>.) Perhaps an issue should be created for this. It would be a big change, as it would require a change to pandoc-types, and changes in all writers and readers. So, it couldn't happen soon.

[elotroalex]

Yes! Block elements would be fantastic. At least to avoid the ugly <div class="stanza">. You have my vote.

The sub-ordered list solution is promising. Our only snag would be to design for a collection of poetry where the indents would be irregular across poems. Let me play with a bit and see if that does it.

[elotroalex]

Oh, did you want me to create the issue? Like I mentioned above, I'm hoping to dedicate some of my resources to this in the future.

[ousia]

By the way, I've long thought that we should have a dedicated block element for line blocks. (Currently there is no distinctive representation of line blocks in the AST; instead, line blocks are parsed as paragraphs with line breaks.)

That would be great.

[ghost]

Another important use case for attributes is in emphasis and strong, for example:
*homo sapiens*{.zool}. Useful for making indexes, ecc.

[ousia]

Another important use case for attributes is in emphasis and strong, for example:
*homo sapiens*{.zool}. Useful for making indexes, ecc.

This is _essential_ to have right hyphenation in foreign languages, such as in:

_homo sapiens_{:la}

[ghost]

@ousia Also to selectively transliterate, for example if I mention greek words in greek alphabet but I want to add an option to show them transliterated, or generate the transliteration immediately after the original while building

[jmuheim]

It comes in version 1.16.x.

I soon will get my server updated, and pandoc 1.16 will be on it, but I don't know which sub-version (1.16.0, 1.16.1, etc.).

Is it possible in version 1.16.0 already? I ask because I'm developing some features for a project which heavily relies on this feature, and I must know whether the new server will support it.

[jgm]

No version of pandoc allows adding attributes to all
Markdown elements. They can be added to headers, code
blocks and spans, images, and links only.

+++ Joshua Muheim [Mar 23 16 08:15 ]:

It comes in version 1.16.x.

I soon will get my server updated, and pandoc 1.16 will be on it, but I
don't know which sub-version (1.16.0, 1.16.1, etc.).

Is it possible in version 1.16.0 already? I ask because I'm developing
some features for a project which heavily relies on this feature, and I
must know whether the new server will support it.

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References

1. https://github.com/jgm/pandoc/issues/684#issuecomment-200389302

[jgm]

And divs and spans.

[jmuheim]

It's absolutely ok for me if I can add them to heading elements (e.g. h1).

And is this possible in 1.16.0?

[jgm]

Yes.

+++ Joshua Muheim [Mar 23 16 08:26 ]:

It's absolutely ok for me if I can add them to heading elements (e.g.
h1).

And is this possible in 1.16.0?

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[jmuheim]

Hoorraaayyy!!! :heart:

And how can I create divs and spans from within Pandoc-Markdown?

[mb21]

Reposting here some of my thoughts from an old pandoc-discuss thread. I still think adding adding attributes to all elements is a viable option for pandoc 2.0...

It feels wrong somehow to keep adding Attr to more and more elements.

I know what you mean, but maybe it's just because Attr is kind of a hacky type in itself (a three-tuple and not even newtype). But is there a better alternative to adding Attr to more things? i.e. what would be ideal?

Maybe Attr should ultimately be a GADT with record syntax (GADTs are a GHC-extension that effectively provide subtyping, see https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/data-type-extensions.html#gadt). Something like:

data Attr where
  GeneralAttr :: { uid    :: String              -- unique identifier
                 , cls    :: [String]            -- classes
                 , others :: [(String, String)]  -- key-value pairs for filters etc
                 } -> Attr
  ImageAttr   :: { uid    :: String
                 , cls    :: [String]
                 , width  :: Dimension
                 , height :: Dimension
                 , figure :: Bool
                 , others :: [(String, String)]
                 } -> Attr
  CodeAttr    :: { uid    :: String
                 , cls    :: [String]
                 , lang   :: String
                 , others :: [(String, String)]
                 } -> Attr
  HeaderAttr  :: { uid    :: String
                 , cls    :: [String]
                 , numbered :: Bool
                 , others :: [(String, String)]
                 } -> Attr
  deriving (Show)


nullAttr :: Attr
nullAttr = GeneralAttr "" [] []


-- sample functions


getUid :: Attr -> String
getUid attr = uid attr


getClass :: Attr -> [String]
getClass = cls

[...]

it's probably a tradeoff away from the flexibility of the list of string tuples (which permits arbitrary key value pairs without breaking the API for anyone) towards using Haskell's type system even more and embedding the semantics of the attributes directly in the types. I'd certainly prefer GADTs from a theoretical point of view, but seeing how hard it is to change pandoc-types I'm not so sure anymore (though future changes to, say, the image attribute would only affect users that make use of the ImageAttr constructor, thus being much more limited in scope). Finally, if we were to stick with dumb key value pairs, should we at least make it a HashMap?

---

@jgm mentioned recently somewhere that we should at least convert Attr from a type to a newtype. That means changing (ident, cls, kvs) to Attr ident cls kvs in lots and lots of places, or is there an unorthodox way around this?

---

Basically, the question still is: what would be the optimal approach of handling attributes? So we can get it as right as possible this time.

[jgm]

+++ Mauro Bieg [Jan 23 17 00:58 ]:

Reposting here some of my thoughts from an old [1]pandoc-discuss
thread. I still think adding adding attributes to all elements is a
viable option for pandoc 2.0...

The question is how to do this without super-extensive and
painful code changes in the entire pandoc code base, and
without making things that were simple before complicated.

Matthew Pickering has suggested we could use pattern
synonyms to keep things simple, and I haven't looked into
that much.

A newtype wrapping a HashMap would make sense, I suppose,
but one advantage of the present representation is that it's
very easy to pattern match.

[mb21]

Matthew Pickering has suggested we could use pattern
synonyms to keep things simple, and I haven't looked into
that much.

I've quickly read Pain Free Unfix with Pattern Synonyms, but not sure how to apply this to our use case... @mpickering ?

[ickc]

Another thing is the AST output: if all elements receives attributes, it will be quite annoying to read the AST where most of them contain ("",[],[]). Is it possible to suppress these?

[tarleb]

I added attributes to all types for my huskydoc experiment, and used patterns to recover a pandoc-like API. It's a nice way to hide implementation details (e.g. the empty attributes mentioned by @ickc), but sometimes felt a bit clunky. However, it's quite possible that I was simply using them wrong.

[xihh87]

For paragraph elements, the attributes can be sent to a newline of its own:

This is a paragraph where we want to aply special attributes.
{#id .class}

I think this is readable enough.

[ousia]

@xihh87, why do you write attributes placed after the text and not before it?

I mean, the following would be more consistent with:

````{#id .class}
a = 2
````

[xihh87]

@ousia code blocks are the only elements that have their attributes before and not after, images, links, headers all have attributes afterwards.

![link text](url alt-text){#id attrs}

# header {#id attrs}

I also think having the attributes at the end is more readable.

[fmatheus]

So, how about been the last thing in the same line with one or more spaces
before like header? {#id question}

On Wednesday, January 25, 2017, xihh87 [e-mail] wrote:

@ousia https://github.com/ousia code blocks are the only elements that
have their attributes before and not after, images, links, headers all have
attributes afterwards.

{#id attrs}

header {#id attrs}

I also think having the attributes at the end is more readable.

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[mb21]

Note the corresponding discussion over at talk.commonmark.org...

[ousia]

@xihh87, except headings, all other elements with attributes are inline ones.

And even if headings are block elements, they may only contain a line (they aren’t a standard block element in Markdown).

Placing attributes at the beginning is clearer with multiple lines in the paragraph:

{#met-I-1}
πάντες ἄνθρωποι τοῦ εἰδέναι ὀρέγονται φύσει. σημεῖον δ᾽ ἡ τῶν αἰσθήσεων
ἀγάπησις· καὶ γὰρ χωρὶς τῆς χρείας ἀγαπῶνται δι᾽ αὑτάς, καὶ μάλιστα τῶν
ἄλλων ἡ διὰ τῶν ὀμμάτων. οὐ γὰρ μόνον ἵνα πράττωμεν ἀλλὰ καὶ μηθὲν
μέλλοντες πράττειν τὸ ὁρᾶν αἱρούμεθα ἀντὶ πάντων ὡς εἰπεῖν τῶν ἄλλων.
αἴτιον δ᾽ ὅτι μάλιστα ποιεῖ γνωρίζειν ἡμᾶς αὕτη τῶν αἰσθήσεων καὶ
πολλὰς δηλοῖ διαφοράς. φύσει μὲν οὖν αἴσθησιν ἔχοντα γίγνεται τὰ ζῷα,
ἐκ δὲ ταύτης τοῖς μὲν αὐτῶν οὐκ ἐγγίγνεται μνήμη, τοῖς δ᾽ ἐγγίγνεται.
καὶ διὰ τοῦτο ταῦτα φρονιμώτερα καὶ μαθητικώτερα τῶν μὴ δυναμένων
μνημονεύειν ἐστί, φρόνιμα μὲν ἄνευ τοῦ μανθάνειν ὅσα μὴ δύναται τῶν
ψόφων ἀκούειν （οἷον μέλιττα κἂν εἴ τι τοιοῦτον ἄλλο γένος ζῴων ἔστι）,
μανθάνει δ᾽ ὅσα πρὸς τῇ μνήμῃ καὶ ταύτην ἔχει τὴν αἴσθησιν. τὰ μὲν οὖν
ἄλλα ταῖς φαντασίαις ζῇ καὶ ταῖς μνήμαις, ἐμπειρίας δὲ μετέχει μικρόν·
τὸ δὲ τῶν ἀνθρώπων γένος καὶ τέχνῃ καὶ λογισμοῖς. γίγνεται δ᾽ ἐκ τῆς
μνήμης ἐμπειρία τοῖς ἀνθρώποις· αἱ γὰρ πολλαὶ μνῆμαι τοῦ αὐτοῦ
πράγματος μιᾶς ἐμπειρίας δύναμιν ἀποτελοῦσιν.

Because you don’t need to search at the end of the paragraph which the attributes are (if any), it is clearer for both the reader and the writer.

Both SGML and XML place attributes for both inline and block elements in the opening tag (never in the closing one).

@fmatheus, consider that headings must contained in only one line. This is required only for this block element.

[jgm]

I think the cleanest approach from a parsing perspective
would be:

• for inline elements, attribute comes immediately after
• for block elements, attribute comes immediately before,
  and on a line by itself

That helps prevent any confusion about whether an attribute
belongs to a block or an inline in the block.

Of course, we've already followed a different path with
headers and code blocks, as noted.

[fmatheus]

I think than before for blocks favors also human reader. Missing why
needs to be a line by itself, isn't before (blocks) and after (inlines)
sufficient?

How to highlight inline blocks? I'm interested in the use case where many
reviewers can highlight/comment pieces of an paragraph.

Em qui, 26 de jan de 2017 08:05, John MacFarlane [e-mail]
escreveu:

I think the cleanest approach from a parsing perspective
would be:

• for inline elements, attribute comes immediately after
• for block elements, attribute comes immediately before,
  and on a line by itself

That helps prevent any confusion about whether an attribute
belongs to a block or an inline in the block.

Of course, we've already followed a different path with
headers and code blocks, as noted.

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[jgm]

+++ fmatheus [Jan 26 17 02:44 ]:

I think than before for blocks favors also human reader. Missing why
needs to be a line by itself, isn't before (blocks) and after (inlines)
sufficient?

Partly to make parsing easier, but partly because it's
cleaner. The eye can subtract the attributes and everything
looks like its regular Markdown self.

How to highlight inline blocks? I'm interested in the use case where
many
reviewers can highlight/comment pieces of an paragraph.

You can already put square [brackets around inlines and add
attributes]{like="this"}.

[xihh87]

John MacFarlane [e-mail] writes:

I think the cleanest approach from a parsing perspective
would be:

• for inline elements, attribute comes immediately after
• for block elements, attribute comes immediately before,
  and on a line by itself

I like this, i think it's both readable and cleaner than my proposal.

[ousia]

• for block elements, attribute comes immediately before,
  and on a line by itself

Of course, we've already followed a different path with
headers and code blocks, as noted.

@jgm, do you you really think that the first example is inherently more readable than the second one:

{#met-I-1}
> πάντες ἄνθρωποι τοῦ εἰδέναι ὀρέγονται φύσει. 

> {#met-I-1}
> πάντες ἄνθρωποι τοῦ εἰδέναι ὀρέγονται φύσει. 

I mean, having an attributes referring to the element in the next line may be easier to be parsed (I simply don’t know), but attributes belong to elements. Writing them before the opening characters doesn’t seem to me especially clear for reading.

Of course, we've already followed a different path with
headers and code blocks, as noted.

Will the way of marking the attribute for these two block elements remain the same after all elements are granted attributes?

[jgm]

+++ Pablo Rodríguez [Jan 27 17 09:23 ]:

I mean, having an attributes referring to the element in the next line
may be easier to be parsed (I simply don’t know), but attributes belong
to elements. Writing them before the opening characters doesn’t seem to
me especially clear for reading.

I don't find that, myself. And anyway, writing it before
the opening > is essential if you want to distinguish
between the case where the attribute is on the blockquote
and the case where it's on the first paragraph inside
the blockquote.

Will the way of marking the attribute for these two block elements
remain the same after all elements are granted attributes?

I don't even know, yet, if it will ever happen that all
elements are granted attributes.

[ousia]

I mean, having an attributes referring to the element in the next line
may be easier to be parsed (I simply don’t know), but attributes belong
to elements. Writing them before the opening characters doesn’t seem to
me especially clear for reading.

I don't find that, myself. And anyway, writing it before
the opening > is essential if you want to distinguish
between the case where the attribute is on the blockquote
and the case where it's on the first paragraph inside
the blockquote.

I overlooked it was side-marking. What would happen with proper division syntax?

I mean, do you really think that the first sample is more readable than the second one?

{#metaphysics-greek}
:::
πάντες ἄνθρωποι τοῦ εἰδέναι ὀρέγονται φύσει. 

ὅτι μὲν οὖν ἡ σοφία περί τινας ἀρχὰς καὶ αἰτίας ἐστὶν ἐπιστήμη, δῆλον.
:::

::: {#metaphysics-greek}
πάντες ἄνθρωποι τοῦ εἰδέναι ὀρέγονται φύσει. 

ὅτι μὲν οὖν ἡ σοφία περί τινας ἀρχὰς καὶ αἰτίας ἐστὶν ἐπιστήμη, δῆλον.
:::

At least for me, the second is clearer that the first sample.

[stroobandt]

Having asked for universal element attributes early on, I would like to chime in.
I tend to agree with @ousia and others, that the syntax for such a feature needs to be chosen with care and I applaud their constructive comments.

Personally, I feel one should try to mimic the way inline CSS classes and IDs are defined in (X)HTML; that is right besides (and inside) of the element declaring tag.

After all, that part of the Pandoc audience who are interested in this new feature, probably are so because they have CSS and (X)HTML in the back of their mind. —At least, I do!—

Finally, here is a Pandoc Markdown excerpt where I would potentially employ element attributes, possibly nested. There is a heading, a hyperlink, that is actually an image, and the hyperlink is also part of a the definition term to definition data. This is why I think the suggestion @ousia makes more sense.

#Win-Test
[![Win-Test](../images/win-test.png)](http://www.win-test.com/)Win-Test
:   The story behind [Win-Test](http://www.win-test.com/) is absolutely fascinating. Win-Test appears to be developed by a handful of French rocket scientists who, in their 35-hour work week, apparently had too much time on their hands waiting for the next rocket launch.

EDIT: Personally, I use Pandoc in many other use cases besides XHTML; anything from writing formal letters and scientific papers in LaTeX to technical reports and contracts in ConTeXt. Only in these use cases, for me personally, I would probably be less compelled to use element attributes —but I certainly would not exclude it. Things should work fine independently of the intended Pandoc use case.

[thriveth]

My use case for attributes is not (X)HTML, but being able to more easily
write my scientific papers in Pandoc's markdown. Being able to set
attributes would mean one could use e.g. the custom table and figure
environments of some journals while still writing pandoc that would
export valid HTML and, not least, to be able to minimize the manual work
in .tex files, ideally eliminate it completely (it is already almost
possible with Scholdoc, but that has its own problems).

On 02/03/2017 01:38 PM, Serge Y. Stroobandt wrote:
>

Having asked for universal element attributes early on, I would like
to chime in.
I tend to agree with @ousia https://github.com/ousia and others,
that the syntax for such a feature needs to be chosen with care and I
applaud their constructive comments.

Personally, I feel one should try to mimic to the way inline CSS
classes and IDs are defined in (X)HTML; that is right after and
inside of the element declaring tag.

After all, that part of the Pandoc audience who are interested in this
new feature, probably are so because they have CSS and (X)HTML in the
back of their mind. ---At least, I do!---

Finally, here is a Pandoc Markdown excerpt where I would potentially
employ element attributes, possibly nested. There is a heading, a
hyperlink, that is actually an image, and the hyperlink is also part
of a the definition term to definition data. This is why I think the
suggestion @ousia https://github.com/ousia makes more sense.

|#Win-Test
Win-Test
: The story behind Win-Test is absolutely
fascinating. Win-Test appears to be developed by a handful of French
rocket scientists who, in their 35-hour work week, apparently had too
much time on their hands waiting for the next rocket launch. |

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[ickc]

My use case for attributes is not (X)HTML, but being able to more easily
write my scientific papers in Pandoc's markdown. Being able to set
attributes would mean one could use e.g. the custom table and figure
environments of some journals while still writing pandoc that would
export valid HTML and, not least, to be able to minimize the manual work
in .tex files, ideally eliminate it completely (it is already almost
possible with Scholdoc, but that has its own problems).

Agree.

Since you mention Scholdoc, I personally think the biggest problem it has is that it takes the shortcut. So by design pandoc is a "Universal markup converter" that concerns all markups (it supports). Many issues in the design of pandoc might disappeared if one restricts the attention to only a few formats.

And it's related to this issue: I think if all elements are granted attributes, it will be easier for 3rd parties to build on top of pandoc rather than forking pandoc. I didn't study Scholdoc in details to see what's necessary to implements all of its features as a filter/custom reader&writer though.

[jgm]

I think that you can do pretty much everything scholdoc does
using vanilla pandoc plus the pandoc-crossref filter.

[thriveth]

I do not want to hijack the thread about this - I don't think pandoc
does everything Scholdoc does. I realize this is a matter of different
design goals - Scholdoc's greater convenience for my use case comes at
the cost of a loss of generality, and Scholdoc admits to being a hack-y
solution to some often demanded features for academic writing until
pandoc or a similar tool can do the same things as conveniently.

I agree with the previous poster who said that adding attributes to all
or almost all elements would make it possible to extend pandoc rather
than fork it, which I think is by far the preferable solution.

But most of all, my comment was meant to emphasize that although Makdown
was originally born with (x)HTML in mind, it is certainly not the only
use case for it today, and solutions that require raw HTML code should
be seen with suspicion.

On 02/04/2017 10:28 AM, John MacFarlane wrote:

I think that you can do pretty much everything scholdoc does
using vanilla pandoc plus the pandoc-crossref filter.

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[stroobandt]

@thriveth Just to make sure there are no misunderstandings; I am not proposing any raw (X)HTML for adding attributes to elements.

All I am trying to convey is that putting attribute declarations on the same line, immediately after block element declarations in Pandoc, may feel more natural to people who also know (X)HTML. Putting attributes on a line immediately above of block element declaration would probably be less so and might perhaps lead to nesting issues/confusion. Anyhow, this needs to be tested with convoluted Pandoc Markdown examples like the one I gave in my previous posting.

I totally respect users who do not use (X)HTML. As a matter of fact, personally, I employ Pandoc to produce a wide array of documents in LaTeX or ConTeXt.

[thriveth]

@stroobandt I apologize, I did not express myself very well. The last part of my former comment was really with pandoc-crossref in mind, but that was not what we were talking about in this thread. Sorry for the confusion and derailing caused by this.

I think the point I wanted to convey was that attributes on general elements could be useful beyond the (X)HTML+CSS use case, e.g. in building specialized writers or templates or whatever for e.g. Journal-specific LaTeX classes etc.

[mb21]

If I understand @mpickering's proposal correctly, view patterns could help us by providing syntactic sugar for pattern matching on a data type that is only defined by a typeclass.

We could change e.g. CodeBlock Attr String to Attr a => CodeBlock a String, which would leave different readers, writers, filters etc. free to use different concrete data type implementations for attributes (e.g. one using the current (String, [String], [(String, String)]) while others use a Hashmap or GADTs or whatnot). Maybe something along the lines of:

class Attr a where
  ident  :: a -> String
  cls    :: a -> [String]
  lookup :: String -> a -> String
  asPair :: a -> (String, [String], [(String, String)])

What I still fail to understand is how exactly view pattern would help us here (I'll sit down and experiment if I find the time), because from what I can see view patterns help us with sum types, but Attr is a product type.

[mb21]

This would allow for relatively straightforward refactors, for example from

blockToHtml opts (CodeBlock (ident,cls,kvs) rawCode) = do
  ...

to

blockToHtml opts (CodeBlock attr rawCode) = do
  let (ident,cls,kvs) = asPair attr
  ...

[stevekm]

Not sure if this is the right place to ask this, but I am trying to customize the interactive elements that are added when converting R Markdown to HTML, specifically the 'tabsets' and floating table of contents. For example, if I wanted to adjust the color of the text in the floating table of contents, I can add CSS to my R Markdown, like this:

title: "Untitled"
output:
  html_document:
    keep_md: true
    css: styles.css
    toc: true
    toc_float: true
    number_sections: true

---
<style type="text/css">
#TOC {
  color: purple; 
}

</style>

example output here

I also want to change to colors of the highlighted item in the floating ToC and tab-buttons the same way. But I have not been able to find any documentation on how to access these features. Is this kind of customization available? I know that if I specify a theme in my YAML header, all the elements change color, so there must be a setting somewhere that I can access via CSS inline in the Markdown, right?

[mb21]

@stevekm No, this is not the right place. Use the pandoc-discuss mailing list for pandoc-related questions. Not sure where the best place for R markdown questions is.

[stevekm]

@mb21 R Markdown is using pandoc, are these elements not generated by it?

[ickc]

@stevekm

Not sure if this is the right place to ask this

It cannot be more wrong:

1. the title is "Permit adding attributes to all Markdown elements". And if you don't know what that means you can read the original post. And then you'll find that it is totally unrelated to what you asked.

2. Not only it does not fall in this issue, it won't be an "issue" on GitHub (pandoc community does not use the issue tracker as forum, a mistake I made in the past).

3. Regarding to

   R Markdown is using pandoc, are these elements not generated by it?

   Will it fall in pandoc-discuss? You can try. What @mb21 is saying is, while Rmarkdown uses pandoc, it is not pure pandoc markdown, and people here generally do not know what Rmarkdown added/changed. If I were you, I might start talking to the Rmarkdown people first.

[jgm]

I'm not sure what you mean by "tabsets" and "floating table
of contents," so I assume these are elements added by R
Markdown. You'll get better help from R Markdown people,
and if there's a pandoc-related issue they can't answer,
they can probably help refine the question to ask here.

[mb21]

The longer I think about a new attribute type, the more I favour a simple solution. What distinguishes attributes from first-class fields in the pandoc ADT (e.g. like the level number for Header)? It's mostly that they are optional and often not filled in, so a hypothetical record type would consist of a lot of Maybes. They also serve the function to bind any extra information to the element to be used e.g. in filters (that's why I'm still in favour of adding Attr to all elements). So maybe going with a practical solution like the following is the best we can do:

data Attr = Attr String [String] (M.Map String String)

Finally, we could add some (lens-like) functions to Builder to construct / modify attributes and discourage direct use of the type which would make future changes to it easier...

[dhimmel]

Table & Equation Attributes?

+1 for the ability to add attributes to additional markdown elements. As of Pandoc version 2.7, it appears from the docs that attributes are supports for headers, code blocks, inline code, links (includes images / figures), divs, and spans.

Attributes are not supported however for tables and equations, which I believe is causing several users trouble (see https://github.com/tomduck/pandoc-tablenos/issues/11, this SO, etcetera). Setting anchors for tables and equations is one main use case that comes to mind. Currently, the pandoc-crossref, pandoc-tablenos, and pandoc-eqnos filters must use hacks to anchor tables/equations, since no id is written to the <table> element in the HTML output. Furthermore, it would be helpful to apply custom classes for styling tables.

So while universal attribute support would be great, is it possible table / equation attribute support could be added in the shorter-term, with a syntax that could be forward compatible?

[despresc]

This might be something worth picking up again (for IR support), now that the CommonMark reader has support for adding attributes to all elements.

Having a new Attr type like was proposed above would be feasible as well:

data Attr = Attr Text [Text] (Map Text Text)
-- or
data Attr = Attr
  { attrId :: Text
  , attrClasses :: [Text]
  , attrKeyVals :: Map Text Text
  }
-- The Map could be newtyped, as was suggested above

That kind of simple Attr type change would be easiest for refactoring (except for keeping the old key-value representation, but I think changing to Map is reasonable).

As for Attr use changes, I think everything in Inline and Block should get an Attr except Plain, Null, Str, Space, SoftBreak, and LineBreak. The Caption type should also get an Attr.

Possibly Plain should get an Attr? It doesn't make sense in the supported formats, but a filter writer might want it for some reason. (Though by that logic Null could get an Attr too).

Initial pandoc support would mostly consist of a lot of simple pattern-match changes, maybe aided by a conversion function to the old Attr type if that changes. Support could be added later in the HTML input and output (and elsewhere, but that's the easiest, I imagine).

[despresc]

An enhancement here is to have

data ListItem = ListItem Attr [Block]
data ListLabel = ListLabel Attr [Inline]

for the lists to use, since in LaTeX these can be labelled and referenced (list items can at least), and in HTML they are elements with the usual attributes. These seem to be the only things that are plausibly Attr-supporting but don't now have a type for Attr to be added. Well, a LineBlock could be a list of Line, I suppose.