Leading and trailing non-whitespace Unicode whitespace is stripped from paragraphs

[ScottAbbey]

The CommonMark dingus implementation currently strips non-whitespace Unicode whitespace from
the start and end of paragraphs. The CommonMark specification and the cmark implementation seem to indicate that these characters should not be stripped.

Example link

Each "space" character in this example is U+1680, OGHAM SPACE MARK, chosen from the list of Unicode whitespace characters that are not in the list of whitespace characters.

Note that the leading and trailing U+1680 characters have been trimmed from the final result.

From CommonMark 0.28, section 4.8:

The paragraph’s raw content is formed by concatenating the lines and removing initial and final [whitespace].

By comparison, in cmark 0.28.3:

Input:

 o o 
 o o 

Output:

<p> o o 
 o o </p>

Ref: commonmark/commonmark-spec#465