[lprnmns]

When a tab separates the opening code fence from its info string, the info string keeps the tab and the language is lost:

$ printf '```\truby\ndef foo(x)\n```\n' | md2html
<pre><code>def foo(x)
</code></pre>

The spec says the text after the fence "is trimmed of leading and trailing spaces or tabs and called the info string" (4.5), so commonmark.js gives <pre><code class="language-ruby">. md_setup_fenced_code_detail() only skipped spaces, so det->info started with the tab, and the det->lang scan stopped right away at that whitespace, which left an empty language. A trailing tab ended up in det->info the same way.

The fix trims with ISBLANK() (space or tab) on both ends. md_is_opening_code_fence() doesn't need a change since it only looks for the end of the line and for backticks.

I added a "Tabs around the fenced code info string" section to test/regressions.txt, with a tab before the info string and a mix of spaces and tabs on both sides. Both examples fail without the change. spec.txt, coverage.txt, regressions.txt and the spec-*.txt suites all pass with md2html built from this branch.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.33%. Comparing base (f9e5eb2) to head (656e4df).

Files with missing lines	Patch %	Lines
src/md4c.c	0.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #468      +/-   ##
==========================================
+ Coverage   79.30%   79.33%   +0.02%     
==========================================
  Files           5        5              
  Lines        3929     3929              
  Branches     1311     1311              
==========================================
+ Hits         3116     3117       +1     
+ Misses        295      294       -1     
  Partials      518      518              

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