Add support for % comments

[xymostech]

No description provided.

[sophiebits]

mrrh?

[alexirpan]

Poking this. It turns out the kramdown engine turns 0 < 1 into

% <![CDATA[
0 < 1 %]]> 

The intention is that it gets wrapped to properly escape the < sign, and the wrapping gets commented out in the rendering.

kramdown is the main markdown engine for Github Pages, so this is a barrier for setting up KaTeX on blogs hosted there.

[sophiebits]

That's clever. CDATA isn't even valid in HTML5 though (only SVG and MathML): https://html.spec.whatwg.org/#cdata-sections.

[meygerjos]

Kramdown has a workaround now. But KaTeX should still fix this.

[kevinbarabash]

I was thinking of pre-processing the input to remove the comments, but we probably don't want to do that b/c then an error reporting would have the wrong position information.

[edemaine]

Can't this be done in the Lexer? Just add comment pattern to the regex, but don't return upon a comment match.

[kevinbarabash]

I think %[^\n]*\n should do the trick.

[xsznix]

Perhaps %[^\n]*(?:\n|$) so that it allows comments at the end of the expression?

[sophiebits]

%.*?\n? is also equivalent to @xsznix's in case you need more ways to do this.

My "mrrh?" comment was ambivalence about the correct answer. I'm not sure it makes sense to allow it at the end of an expression – since you can't do $x%y$ in TeX without a newline. Maybe it does.

[kevinbarabash]

pdflatex throws an error in that situation which means that people copy TeX code into KaTeX won't be include code with comments like that. Things might go wrong copy/pasting a KaTeX string back into a .tex file, but users will have to modify the string anyways by add $. If we support comments a person should be able to type a^2 + b^2 = c^2 %% Pythagoras' theorem into a text input and have that work without having to add a newline at the end of it before they pass it to katex. My vote would be to allow comments without a newline at the end of the string.

[sophiebits]

The fact that this exists feels like a small argument in favor of not supporting ending comments:

https://github.com/Khan/KaTeX/blob/a358c5a94c86a13bd3381334c9ad4ca23cd57781/dockers/texcmp/texcmp.js#L62

[kevinbarabash]

We could change that to

let tex = "$" + itm.tex + "\n$"

😛

[sophiebits]

Yes, but only if you're expecting this behavior! The fact that it isn't that already indicates that you wouldn't. Someone else might equally try to build a web writing interface that accepts KaTeX and turns into a full TeX document later and be bitten by this.

[kevinbarabash]

We could have an option to allow comments without newlines, but have the default be strict LaTeX compliance.

[sophiebits]

In Perseus (or auto-render), I also wouldn't want typing $x%y$ to render a mathy x. It's confusing.

What's the value in allowing comments without newlines? If you really want to do that you can always just tack on a newline to the input expression when calling KaTeX.

[edemaine]

IMHO, if $x%y$ causes x%y to get passed into KaTeX, then that's a mistake: that second $ shouldn't be considered a terminator when it's hidden by the comment. Of course, that is how it works now with auto-render, but in my opinion that's a bug in auto-render.

I guess I can't imagine a setting where x%y really makes sense as input to KaTeX, so I'd be OK with requiring a \n at the end of the comment regex.

[kevinbarabash]

I'm okay with that too. The best justification I could come up with is that it would all writing comments in our test app, but that isn't much of a justification. Our test app should be modified to use a <textarea> instead so that it's easy to test comments locally.

[xsznix]

Yeah, it sounds like allowing a comment to end a math expression would not be expected behavior. I rescind my suggestion.

[kevinbarabash]

I'm going to give this a shot.

[kevinbarabash]

[edemaine]

@kevinbarabash <textarea> would be very handy when testing arrays and such, thanks!

You should test spacing behavior:

\text{hello% comment
world}

should parse like \text{helloworld}, but not like

\text{hello% comment

world}

(oops, moving this discussion to #884)