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Add boolean/flag attribute shorthand to attribute syntax #372

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Add boolean/flag attribute shorthand to attribute syntax #372

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13 changes: 13 additions & 0 deletions doc/syntax.md
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Expand Up @@ -331,6 +331,10 @@ Inside the curly braces, the following syntax is possible:
are not needed when the value consists entirely of ASCII alphanumeric
characters or `_` or `:` or `-`. Backslash escapes may be used inside
quoted values.
- A bare `key` (a word consisting of ASCII alphanumeric characters,
`_`, or `-`, not followed by `=`) specifies a boolean attribute. This
is equivalent to `key=""` and maps to HTML boolean attributes such as

@Omikhleia Omikhleia Feb 5, 2026 •
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Really, HTML is one possible output only. If mentioned in a general specification of a markup, it's at best as an example.
This being said, why would it be equivalent to key=""` (an empty string value is not necessarily a boolean in a general context)?

@dereuromark dereuromark Feb 5, 2026 •
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You can also write it as key="key"
The HTML5 specs are interesting here, and a bit weird at first glance for sure.
But they bool concept is quite handy and useful in such places here. I think it also works as agnostic one, or translated well enough to it.

@Omikhleia Omikhleia Feb 5, 2026

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Hmm... the only agnostic and semantically clear way would be, for me, key (standalone) being equivalent to key=true.
A HTML renderer may interpret key=true as key in output, and remove key=false, but that's an HTML concept (that doesn't really makes any sense beyond a weird historical reason from SGML to HTML etc.). No?

@dereuromark dereuromark Feb 5, 2026

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The good thing about the bool attr is that we do not need to care about the verbose form per "end use", incl HTML. We just use the simple bool form and it just works tm :)

@Omikhleia Omikhleia Feb 6, 2026

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And key="" is really what it is, an empty string (not simplified)

@dereuromark dereuromark Feb 6, 2026 •
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There is no need at this point to debate this.
The bool attribute is exactly why this discussion becomes void then, solving it cleanly.

@Omikhleia Omikhleia Feb 6, 2026

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There is no need at this point to debate this.

I am not sure I understand what you mean here, the PR says:

This is equivalent to key=""

I don't think this has to be the case. And if not debated now (for some reason), then it shouldn't be mentioned. Or did I miss the point?

@dereuromark dereuromark Feb 6, 2026

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Yes ignore that part. That's html5 specific and not relevant for General usage. My bad.

`disabled`, `hidden`, `reversed`, `open`, and `download`.
- `%` begins a comment, which ends with the next `%` or the end of the
attribute (`}`).

Expand All @@ -350,6 +354,15 @@ is the same as

avant{lang=fr .blue}

Boolean attributes can be combined freely with other attribute types:

[Download](file.zip){download .btn}

{reversed}
1. Third
2. Second
3. First

## Block syntax

As in commonmark, block structure can be discerned prior to inline
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