Text between < and > that looks like an HTML tag is parsed as a raw HTML tag and will be rendered in HTML without escaping. Tag and attribute names are not limited to current HTML tags, so custom tags (and even, say, DocBook tags) may be used.
Here is the grammar for tags:
tag name consists of an ASCII letter followed by zero or more ASCII letters, digits, or hyphens (-).

An attribute consists of whitespace, an attribute name, and an optional attribute value specification.

An attribute name consists of an ASCII letter, _, or :, followed by zero or more ASCII letters, digits, _.:, or -. (Note: This is the XML specification restricted to ASCII. HTML5 is laxer.)

An attribute value specification consists of optional whitespace, a = character, optional whitespace, and an attribute value.

An attribute value consists of an unquoted attribute value, a single-quoted attribute value, or a double-quoted attribute value.

An unquoted attribute value is a nonempty string of characters not including whitespace"'=<>, or `.

single-quoted attribute value consists of ', zero or more characters not including ', and a final '.

double-quoted attribute value consists of ", zero or more characters not including ", and a final ".

An open tag consists of a < character, a tag name, zero or more attributes, optional whitespace, an optional / character, and a > character.

closing tag consists of the string </, a tag name, optional whitespace, and the character >.

An HTML comment consists of <!-- + text + -->, where text does not start with > or ->, does not end with -, and does not contain --. (See the HTML5 spec.)

processing instruction consists of the string <?, a string of characters not including the string ?>, and the string ?>.

declaration consists of the string <!, a name consisting of one or more uppercase ASCII letters,whitespace, a string of characters not including the character >, and the character >.

CDATA section consists of the string <![CDATA[, a string of characters not including the string ]]>, and the string ]]>.

An HTML tag consists of an open tag, a closing tag, an HTML comment, a processing instruction, a declaration, or a CDATA section.

Here are some simple open tags:

Example 632

Markdown HTML Demo


Empty elements:

Example 633

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Whitespace is allowed:

Example 634

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<a  /><b2
data="foo" >

<p><a  /><b2
data="foo" ></p>

With attributes:

Example 635

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<a foo="bar" bam = 'baz <em>"</em>'
_boolean zoop:33=zoop:33 />

<p><a foo="bar" bam = 'baz <em>"</em>'
_boolean zoop:33=zoop:33 /></p>

Custom tag names can be used:

Example 636

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Foo <responsive-image src="foo.jpg" />

<p>Foo <responsive-image src="foo.jpg" /></p>

Illegal tag names, not parsed as HTML:

Example 637

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<33> <__>

<p>&lt;33&gt; &lt;__&gt;</p>

Illegal attribute names:

Example 638

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<a h*#ref="hi">

<p>&lt;a h*#ref=&quot;hi&quot;&gt;</p>

Illegal attribute values:

Example 639

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<a href="hi'> <a href=hi'>

<p>&lt;a href=&quot;hi'&gt; &lt;a href=hi'&gt;</p>

Illegal whitespace:

Example 640

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< a><
foo><bar/ >
<foo bar=baz
bim!bop />

<p>&lt; a&gt;&lt;
foo&gt;&lt;bar/ &gt;
&lt;foo bar=baz
bim!bop /&gt;</p>

Missing whitespace:

Example 641

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<a href='bar'title=title>

<p>&lt;a href='bar'title=title&gt;</p>

Closing tags:

Example 642

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</a></foo >

<p></a></foo ></p>

Illegal attributes in closing tag:

Example 643

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</a href="foo">

<p>&lt;/a href=&quot;foo&quot;&gt;</p>


Example 644

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foo <!-- this is a
comment - with hyphen -->

<p>foo <!-- this is a
comment - with hyphen --></p>

Example 645

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foo <!-- not a comment -- two hyphens -->

<p>foo &lt;!-- not a comment -- two hyphens --&gt;</p>

Not comments:

Example 646

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foo <!--> foo -->

foo <!-- foo--->

<p>foo &lt;!--&gt; foo --&gt;</p>
<p>foo &lt;!-- foo---&gt;</p>

Processing instructions:

Example 647

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foo <?php echo $a; ?>

<p>foo <?php echo $a; ?></p>


Example 648

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<p>foo <!ELEMENT br EMPTY></p>

CDATA sections:

Example 649

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foo <![CDATA[>&<]]>

<p>foo <![CDATA[>&<]]></p>

Entity and numeric character references are preserved in HTML attributes:

Example 650

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foo <a href="&ouml;">

<p>foo <a href="&ouml;"></p>

Backslash escapes do not work in HTML attributes:

Example 651

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foo <a href="\*">

<p>foo <a href="\*"></p>

Example 652

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<a href="\"">

<p>&lt;a href=&quot;&quot;&quot;&gt;</p>