Vega-lite: Refactor: extract special Expression type

[kanitw]

So we can link it to the parameter type page just like we do with color.

• [ ] condition
• [ ] labelExpr
• [ ] filter
• [ ] calculate

[adrijshikhar]

@kanitw is this issue still open?

[kanitw]

Yes, right now all expression just have type strings, which are not distinguished from arbitrary strings.

It'd be nice to do treat them slightly different, just like what we do with Color.

[adrijshikhar]

Thanks for your reply. This is my first issue, so can you guide me a bit on what is required. I have already setup the repo.

[kanitw]

I'll search for the type Color and see how it's being used. Then you'd want to do the same thing with expression for properties listed above.