
# Permissive WWW Autolinks

With the flag `MD_FLAG_PERMISSIVEWWWAUTOLINKS`, MD4C enables recognition of
autolinks starting with `www.`, even if they do not exactly follow the syntax
of autolink as specified in CommonMark specification.

These do not have to be enclosed in `<` and `>`, and they even do not need
any preceding scheme specification.

The WWW autolink will be recognized when the text `www.` is found followed by a
valid domain. A valid domain consists of segments of alphanumeric characters,
underscores (`_`) and hyphens (`-`) separated by periods (`.`). There must be
at least one period, and no underscores may be present in the last two segments
of the domain.

The scheme `http` will be inserted automatically:

```````````````````````````````` example
www.commonmark.org
.
<p><a href="http://www.commonmark.org">www.commonmark.org</a></p>
````````````````````````````````

After a valid domain, zero or more non-space non-`<` characters may follow:

```````````````````````````````` example
Visit www.commonmark.org/help for more information.
.
<p>Visit <a href="http://www.commonmark.org/help">www.commonmark.org/help</a> for more information.</p>
````````````````````````````````

We then apply extended autolink path validation as follows:

Trailing punctuation (specifically, `?`, `!`, `.`, `,`, `:`, `*`, `_`, and `~`)
will not be considered part of the autolink, though they may be included in the
interior of the link:

```````````````````````````````` example
Visit www.commonmark.org.

Visit www.commonmark.org/a.b.
.
<p>Visit <a href="http://www.commonmark.org">www.commonmark.org</a>.</p>
<p>Visit <a href="http://www.commonmark.org/a.b">www.commonmark.org/a.b</a>.</p>
````````````````````````````````

When an autolink ends in `)`, we scan the entire autolink for the total number
of parentheses.  If there is a greater number of closing parentheses than
opening ones, we don't consider the last character part of the autolink, in
order to facilitate including an autolink inside a parenthesis:

```````````````````````````````` example
www.google.com/search?q=Markup+(business)

(www.google.com/search?q=Markup+(business))
.
<p><a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a></p>
<p>(<a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a>)</p>
````````````````````````````````

This check is only done when the link ends in a closing parentheses `)`, so if
the only parentheses are in the interior of the autolink, no special rules are
applied:

```````````````````````````````` example
www.google.com/search?q=(business))+ok
.
<p><a href="http://www.google.com/search?q=(business))+ok">www.google.com/search?q=(business))+ok</a></p>
````````````````````````````````

If an autolink ends in a semicolon (`;`), we check to see if it appears to
resemble an [entity reference][entity references]; if the preceding text is `&`
followed by one or more alphanumeric characters.  If so, it is excluded from
the autolink:

```````````````````````````````` example
www.google.com/search?q=commonmark&hl=en

www.google.com/search?q=commonmark&hl;
.
<p><a href="http://www.google.com/search?q=commonmark&amp;hl=en">www.google.com/search?q=commonmark&amp;hl=en</a></p>
<p><a href="http://www.google.com/search?q=commonmark">www.google.com/search?q=commonmark</a>&amp;hl;</p>
````````````````````````````````

`<` immediately ends an autolink.

```````````````````````````````` example
www.commonmark.org/he<lp
.
<p><a href="http://www.commonmark.org/he">www.commonmark.org/he</a>&lt;lp</p>
````````````````````````````````


## GitHub Issues

### [Issue 53](https://github.com/mity/md4c/issues/53)
```````````````````````````````` example
This is [link](www.github.com/).
.
<p>This is <a href="www.github.com/">link</a>.</p>
````````````````````````````````
```````````````````````````````` example
This is [link](www.github.com/)X
.
<p>This is <a href="www.github.com/">link</a>X</p>
````````````````````````````````
