Em is a limited hypertext markup language that is designed to be maximally readable. It is similar to Markdown, but it has a few key advantages:

1. It is more readable.
2. It is simpler to parse.
3. There is not more than one way to do it: for any given HTML, there is never more than a single possible em representation.

Em values readability over expressiveness. This means that it is rather limited in terms of what HTML it can produce. Most noticeably, only a very limited form of inline links are supported (see Hyperlinks below).

Em also values consistency and predictability. As such, the syntax is rather strict. This makes it a bit harder to learn, but much more predictable.

Em's complete and exact syntax is defined by its implementation [1], but a general description follows below. For longer examples, see the source code for this text [2] or the test file [3].

Em is implemented in portable awk, with an rc script to bind it together. It is written on and for Plan 9 primarily, but the rc code can (more or less) trivially be translated to POSIX shell; the work just hasn't been done yet.

Em also includes the rc script htwrap, which can be used to create a standalone HTML document from em output.

Inline formatting

Font style

Italic, bold and teletype text is marked with the asterisk, the underscore and the backtick, respectively:

Example of *italic text*, _bold text_ and `teletype text`.

The marks are only valid in certain positions:

1. At word borders
2. At the beginning of a word after an opening parenthesis
3. At the end of a word before any of .,:;?!)
4. At the end of a word before a closing parenthesis followed by any of .,:;?!

Inline references

Inline references are created with square brackets:

Example of an inline reference [1].

 [1] The quick brown fox ...

In the final output, the inline reference becomes a link to the reference item later in the document:

<p>Example of an inline reference [<a href="#ref1">1</a>].
</p>
<ol class="reflist">
<li value="1" id="ref1">The quick brown fox ...
</li>
</ol>

For more information about references, see Reference lists below.

Hyperlinks

Hyperlinks are a special case of inline references. When an inline reference refers to a reference containing a single link, the inline reference points directly to that link, rather than at the reference.

It is available for download [1].

 [1] <./v1.tgz>

The above example translates to the following HTML:

<p>It is available for download [<a href="./v1.tgz">1</a>].
</p>
<ol class="reflist">
<li value="1" id="ref1"><a href="./v1.tgz">./v1.tgz</a>
</li>
</ol>

Block-level formatting

• A single empty line marks a block break. There is no exception to this rule. The line is removed in the final output.
• All blocks support inline formatting, except headings, preformatted blocks and terms in definition lists.
• One block cannot be put within another block. For example, it is impossible to put a paragraph or a preformatted block inside a list item.

Headings

Headings begin and end with the same number of equal signs:

= First-level heading =

== Second-level heading ==

Lists

All lists start with a single space, followed by some marker.

Unordered lists are created with - :

 - This is an unordered list
 - With two items

Ordered lists are created with n. :

 1. This is an ordered list
 2. With an item that spans
two lines

Definition lists are created with term: :

 dinosaur: an animal

Reference lists are created with [n] :

 [1] This is a reference list
 [2] With two items

Nesting

Unordered and ordered lists can be nested. An additional space at the beginning of the line increases the item level by one:

 1. First level
  - Second level
 2. First level

Reference lists

A reference list is a special type of list. It is a type of footnote list, to which you can make inline references:

See footnote [1].

 [1] The quick brown fox ...

Note: There is a special type of reference list item called a hyperlink reference. It contains only a single link:

 [1] <http://example.com>

Hyperlink references behave just like normal references, except inline references to them link directly to the link rather than the reference item.

Preformatted blocks

Preformatted blocks start with a single tab:

	#include <stdio.h>
	main() { puts("Hello world!\n"); }

Paragraphs

Paragraphs start with no space:

This is a paragraph
with two lines.

This is another paragraph.

References

1. ../tree/emparse
2. ../tree/README
3. ../tree/test.em