Strikethrough extension fails if first character within delimiters is punctuation

[jmooring]

A better description...

The strikethrough extension fails if (a) the first character within the delimiters is punctuation, and (b) the character preceding the opening delimiter is either a letter or a number.

Tested with [email protected] playground

Markdown:

K~1~

K~*1~

Expected:

<p>K<del>1</del></p>
<p>K<del>*1</del></p>

Actual:

<p>K<del>1</del></p>
<p>K~*1~</p>

From the specifications (emphasis mine):

Strikethrough text is any text wrapped in a matching pair of one or two tildes (~).

However, note that GitHub has the same problem. The example above rendered by GitHub:

K1

K~*1~

[yuin]

This kind of extensions are implemented as same as the emphasis. CommonMark emphasis algorithm is known for complicated and having many edge cases. Espacially the emphasis algorighm is basically designed for sentences written in Western language(that is separated by spaces), other situations like CJK sentences and math often fail.

I think that GFM spec writes spec wrong(Aside from whether CommonMark emphasis algorithm is good or bad)