I need to change all letters in words to uppercase.
In regex, I use \U or \L and I get the result as in the screenshot. Anyone have an idea what I should enter there?

Regex in .NET doesn't support the \U and \L.
Thanks.
Also, there isn't any substitute.
You can:
For the more frequent errors I defined separate expressions. The rest I corrected manually.
Thanks again.
@OmrSi However, when pasting back to SE, empty lines will be taken into account, not sure if it's something to fix. :-/
@LeonCheung How so? Column paste from clipboard allows you to paste only text and takes the empty lines in the text as an indication to new lines.
I don't know, it shouldn't be like that but just confirmed in the beta 300 and 353.
For the test I made these corrections again. It was working. I copied and pasted from the source view.
Ah oh, it occurs to me even with 3.5.1. I'm soooooo puzzled....

@LeonCheung Just took a look at the code, it actually just pastes every line in a paragraph even if it's empty.
Then how to explain the GIF? 馃ぃ
You missunderstood.
It just takes every line in the copied text and pastes it to a line in the list view.
Meaning if you have:
Line1B
it will paste each line into a list view item, even if the line is a space.
Ah I see. It puzzled me because I tried to follow your idea above step by step, but couldn't get the expected result, so...
That's my bad. I thought it worked that way.
Turned out I just copy the time with the text all the time, so I thought that was the default behavior.
I don't know which is better, tbh.
It's okay just... it reminded me on a specific workflow in real life. Similar to what's mentioned in #1528. Maybe that's another topic.
In the case here, a bit brainstorm can be no harm :) like:

I don't know if Line break is exactly right here, it should be something like lines separator.
Ah yes, you are right.
I need to change all letters in words to uppercase.
Have you tried Tools - Change casing... ?
@niksedk He seems to have a letter at the end of the regex, so I guess he only wants to change certain words?
It is just like OmrSi says. I wanted to uppercase the text between "<<" and "艁". These are descriptions for the hearing impaired, which I wanted to highlight in capital letters and in color. This is how they are presented in alphabetical order.

Edit
I was able to solve my problem only using SE :)
Step 1: I have replaced the characters "<<" and "艁" with brackets "(((" and ")))".
Step 2: I used the HI2UC plug.
Step 3: I replaced the brackets with the color tags.
Boss :P
@borifax Very nice tip. I didn't know that plug-in, and it's very powerful, not sure @ivandrofly can see this.
Here here... maybe have a option in HI2UC to allow user to define token for start&end of HI? /cc @LeonCheung
@ivandrofly Oh then it would definitely be even better if technically possible. :)