.
==Mark==
.
<p><mark>Mark</mark></p>
.

.
x ====foo== bar==
.
<p>x <mark><mark>foo</mark> bar</mark></p>
.

.
x ==foo ==bar====
.
<p>x <mark>foo <mark>bar</mark></mark></p>
.

.
x ====foo====
.
<p>x <mark><mark>foo</mark></mark></p>
.

.
x ===foo===
.
<p>x =<mark>foo</mark>=</p>
.

Marks have the same priority as emphases:

.
**==test**==

==**test==**
.
<p><strong>==test</strong>==</p>
<p><mark>**test</mark>**</p>
.


Marks have the same priority as emphases with respect to links
.
[==link]()==

==[link==]()
.
<p><a href="">==link</a>==</p>
<p>==<a href="">link==</a></p>
.


Marks have the same priority as emphases with respect to backticks
.
==`code==`

`==code`==
.
<p>==<code>code==</code></p>
<p><code>==code</code>==</p>
.


Nested marks
.
==foo ==bar== baz==
.
<p><mark>foo <mark>bar</mark> baz</mark></p>
.


Nested marks with emphasis
.
==f **o ==o b== a** r==
.
<p><mark>f <strong>o <mark>o b</mark> a</strong> r</mark></p>
.


Should not have a whitespace between text and "==":
.
foo == bar == baz
.
<p>foo == bar == baz</p>
.


Newline should be considered a whitespace:
.
==test
== a

==
test==

==
test
==
.
<p>==test
== a</p>
<p>==
test==</p>
<p>==
test
==</p>
.


.
x ==a ==foo===========bar== b==

x ==a ==foo============bar== b==
.
<p>x <mark>a <mark>foo</mark></mark>===<mark><mark>bar</mark> b</mark></p>
<p>x <mark>a <mark>foo</mark></mark>====<mark><mark>bar</mark> b</mark></p>
.


From CommonMark test suite, replacing `**` with our marker:

.
a=="foo"==
.
<p>a==&quot;foo&quot;==</p>
.
