ATX headings

An ATX heading (opens new window) consists of a string of characters, parsed as inline content, between an opening sequence of 1–6 unescaped # characters and an optional closing sequence of any number of unescaped # characters. The opening sequence of # characters must be followed by a space (opens new window) or by the end of line. The optional closing sequence of #s must be preceded by a space (opens new window) and may be followed by spaces only. The opening #character may be indented 0-3 spaces. The raw contents of the heading are stripped of leading and trailing spaces before being parsed as inline content. The heading level is equal to the number of # characters in the opening sequence.

Simple headings:

Example 32

Markdown	HTML	Demo
# foo ## foo ### foo #### foo ##### foo ###### foo	<h1>foo</h1> <h2>foo</h2> <h3>foo</h3> <h4>foo</h4> <h5>foo</h5> <h6>foo</h6>

More than six # characters is not a heading:

Example 33

Markdown	HTML	Demo
####### foo	<p>####### foo</p>

At least one space is required between the # characters and the heading’s contents, unless the heading is empty. Note that many implementations currently do not require the space. However, the space was required by the original ATX implementation (opens new window), and it helps prevent things like the following from being parsed as headings:

Example 34

Markdown	HTML	Demo
#5 bolt #hashtag	<p>#5 bolt</p> <p>#hashtag</p>

This is not a heading, because the first # is escaped:

Example 35

Markdown	HTML	Demo
\## foo	<p>## foo</p>

Contents are parsed as inlines:

Example 36

Markdown	HTML	Demo
# foo *bar* \*baz\*	<h1>foo <em>bar</em> *baz*</h1>

Leading and trailing whitespace is ignored in parsing inline content:

Example 37

Markdown	HTML	Demo
# foo	<h1>foo</h1>

One to three spaces indentation are allowed:

Example 38

Markdown	HTML	Demo
### foo ## foo # foo	<h3>foo</h3> <h2>foo</h2> <h1>foo</h1>

Four spaces are too much:

Example 39

Markdown	HTML	Demo
# foo	<pre><code># foo </code></pre>

Example 40

Markdown	HTML	Demo
foo # bar	<p>foo # bar</p>

A closing sequence of # characters is optional:

Example 41

Markdown	HTML	Demo
## foo ## ### bar ###	<h2>foo</h2> <h3>bar</h3>

It need not be the same length as the opening sequence:

Example 42

Markdown	HTML	Demo
# foo ################################## ##### foo ##	<h1>foo</h1> <h5>foo</h5>

Spaces are allowed after the closing sequence:

Example 43

Markdown	HTML	Demo
### foo ###	<h3>foo</h3>

A sequence of # characters with anything but spaces (opens new window) following it is not a closing sequence, but counts as part of the contents of the heading:

Example 44

Markdown	HTML	Demo
### foo ### b	<h3>foo ### b</h3>

The closing sequence must be preceded by a space:

Example 45

Markdown	HTML	Demo
# foo#	<h1>foo#</h1>

Backslash-escaped # characters do not count as part of the closing sequence:

Example 46

Markdown	HTML	Demo
### foo \### ## foo #\## # foo \#	<h3>foo ###</h3> <h2>foo ###</h2> <h1>foo #</h1>

ATX headings need not be separated from surrounding content by blank lines, and they can interrupt paragraphs:

Example 47

Markdown	HTML	Demo
**** ## foo ****	<hr /> <h2>foo</h2> <hr />

Example 48

Markdown	HTML	Demo
Foo bar # baz Bar foo	<p>Foo bar</p> <h1>baz</h1> <p>Bar foo</p>

ATX headings can be empty:

Example 49

Markdown	HTML	Demo
## # ### ###	<h2></h2> <h1></h1> <h3></h3>