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108 lines
4.0 KiB
108 lines
4.0 KiB
3 years ago
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# Permissive WWW Autolinks
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With the flag `MD_FLAG_PERMISSIVEWWWAUTOLINKS`, MD4C enables recognition of
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autolinks starting with `www.`, even if they do not exactly follow the syntax
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of autolink as specified in CommonMark specification.
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These do not have to be enclosed in `<` and `>`, and they even do not need
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any preceding scheme specification.
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The WWW autolink will be recognized when the text `www.` is found followed by a
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valid domain. A valid domain consists of segments of alphanumeric characters,
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underscores (`_`) and hyphens (`-`) separated by periods (`.`). There must be
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at least one period, and no underscores may be present in the last two segments
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of the domain.
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The scheme `http` will be inserted automatically:
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```````````````````````````````` example
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www.commonmark.org
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.
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<p><a href="http://www.commonmark.org">www.commonmark.org</a></p>
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````````````````````````````````
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After a valid domain, zero or more non-space non-`<` characters may follow:
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```````````````````````````````` example
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Visit www.commonmark.org/help for more information.
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.
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<p>Visit <a href="http://www.commonmark.org/help">www.commonmark.org/help</a> for more information.</p>
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````````````````````````````````
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We then apply extended autolink path validation as follows:
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Trailing punctuation (specifically, `?`, `!`, `.`, `,`, `:`, `*`, `_`, and `~`)
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will not be considered part of the autolink, though they may be included in the
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interior of the link:
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```````````````````````````````` example
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Visit www.commonmark.org.
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Visit www.commonmark.org/a.b.
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.
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<p>Visit <a href="http://www.commonmark.org">www.commonmark.org</a>.</p>
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<p>Visit <a href="http://www.commonmark.org/a.b">www.commonmark.org/a.b</a>.</p>
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````````````````````````````````
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When an autolink ends in `)`, we scan the entire autolink for the total number
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of parentheses. If there is a greater number of closing parentheses than
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opening ones, we don't consider the last character part of the autolink, in
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order to facilitate including an autolink inside a parenthesis:
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```````````````````````````````` example
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www.google.com/search?q=Markup+(business)
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(www.google.com/search?q=Markup+(business))
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.
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<p><a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a></p>
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<p>(<a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a>)</p>
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````````````````````````````````
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This check is only done when the link ends in a closing parentheses `)`, so if
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the only parentheses are in the interior of the autolink, no special rules are
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applied:
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```````````````````````````````` example
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www.google.com/search?q=(business))+ok
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.
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<p><a href="http://www.google.com/search?q=(business))+ok">www.google.com/search?q=(business))+ok</a></p>
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````````````````````````````````
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If an autolink ends in a semicolon (`;`), we check to see if it appears to
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resemble an [entity reference][entity references]; if the preceding text is `&`
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followed by one or more alphanumeric characters. If so, it is excluded from
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the autolink:
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```````````````````````````````` example
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www.google.com/search?q=commonmark&hl=en
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www.google.com/search?q=commonmark&hl;
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.
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<p><a href="http://www.google.com/search?q=commonmark&hl=en">www.google.com/search?q=commonmark&hl=en</a></p>
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<p><a href="http://www.google.com/search?q=commonmark">www.google.com/search?q=commonmark</a>&hl;</p>
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````````````````````````````````
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`<` immediately ends an autolink.
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```````````````````````````````` example
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www.commonmark.org/he<lp
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.
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<p><a href="http://www.commonmark.org/he">www.commonmark.org/he</a><lp</p>
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````````````````````````````````
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## GitHub Issues
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### [Issue 53](https://github.com/mity/md4c/issues/53)
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```````````````````````````````` example
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This is [link](www.github.com/).
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.
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<p>This is <a href="www.github.com/">link</a>.</p>
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````````````````````````````````
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```````````````````````````````` example
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This is [link](www.github.com/)X
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.
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<p>This is <a href="www.github.com/">link</a>X</p>
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````````````````````````````````
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