Lightweight markup languages are used in applications where it may be necessary to read the raw document as well as the final rendered output.
For instance, a person downloading a software library might prefer to read the documentation in a text editor rather than a web browser.
Another application for such languages is to provide for data entry in web-based publishing, such as blogs and wikis, where the input interface is a simple text box.
In 1986 international standard SGML provided facilities to define and parse lightweight markup languages using grammars and tag implication.
Like HTML (bold), some languages use named elements that share a common format for start and end tags (e.g. BBCode [b]bold[/b]), whereas proper lightweight markup languages are restricted to ASCII-only punctuation marks and other non-letter symbols for tags, but some also mix both styles (e.g.
Some markup languages are tailored for a specific purpose, such as documenting computer code (e.g. POD, reST, RD) or being converted to a certain output format (usually HTML or LaTeX) and nothing else, others are more general in application.
[clarification needed] Presentation oriented languages include AsciiDoc, atx, BBCode, Creole, Crossmark, Djot, Epytext, Haml, JsonML, MakeDoc, Markdown, Org-mode, POD (Perl), reST (Python), RD (Ruby), Setext, SiSU, SPIP, Xupl, Texy!, Textile, txt2tags, UDO and Wikitext.
[28] Although usually documented as yielding italic and bold text, most lightweight markup processors output semantic HTML elements em and strong instead.
Quoted computer code is traditionally presented in typewriter-like fonts where each character occupies the same fixed width.
The first style uses underlines, i.e. repeated characters (e.g. equals =, hyphen - or tilde ~, usually at least two or four times) in the line below the heading text.
Most languages also support the reduplication of the markers at the end of the line, but whereas some make them mandatory, others do not even expect their numbers to match.
Hyperlinks can either be added inline, which may clutter the code because of long URLs, or with named alias or numbered id references to lines containing nothing but the address and related attributes and often may be located anywhere in the document.
LMLs that are tailored for special setups, e.g. wikis or code documentation, may automatically generate named anchors (for headings, functions etc.)
Microsoft Word automatically converts paragraphs that start with an asterisk *, hyphen-minus - or greater-than bracket > followed by a space or horizontal tabulator as bullet list items.
The following lightweight markup languages, while similar to some of those already mentioned, have not yet been added to the comparison tables in this article: