Justification for this feature is added in the docs.
Precedent for the precise syntax: Hugo.
Hugo puts this syntax behind a preference named headerIds, and automatic
header ID generation behind a preference named autoHeaderIds, with both
enabled by default. I have not implemented a switch to disable this.
My suggestion for a workaround for the improbable case of desiring a
literal “{#…}” at the end of a header is to replace `}` with `}`.
The algorithm I have used is not identical to [that
which Hugo uses][0], because Hugo’s looks to work at the source level,
whereas here we work at the pulldown-cmark event level, which is
generally more sane, but potentially limiting for extremely esoteric
IDs.
Practical differences in implementation from Hugo (based purely on
reading [blackfriday’s implementation][0], not actually trying it):
- I believe Hugo would treat `# Foo {#*bar*}` as a heading with text
“Foo” and ID `*bar*`, since it is working at the source level; whereas
this code turns it into a heading with HTML `Foo {#<em>bar</em>}`, as
it works at the pulldown-cmark event level and doesn’t go out of its
way to make that work (I’m not familiar with pulldown-cmark, but I get
the impression that you could make it work Hugo’s way on this point).
The difference should be negligible: only *very* esoteric hashes would
include magic Markdown characters.
- Hugo will automatically generate an ID for `{#}`, whereas what I’ve
coded here will yield a blank ID instead (which feels more correct to
me—`None` versus `Some("")`, and all that).
In practice the results should be identical.
Fixes#433.
[0]: a477dd1646/block.go (L218-L234)
