title.txt

The MediaWiki software's "Title" class represents article
titles, which are used for many purposes: as the human-readable
text title of the article, in the URL used to access the article,
the wikitext link to the article, the key into the article
database, and so on. The class in instantiated from one of
these forms and can be queried for the others, and for other
attributes of the title. This is intended to be an
immutable "value" class, so there are no mutator functions.

To get a new instance, call one of the static factory
methods Title::newFromURL(), Title::newFromDBKey(),
or Title::newFromText(). Once instantiated, the
other non-static accessor methods can be used, such as
getText(), getDBKey(), getNamespace(), etc.

The prefix rules: a title consists of an optional interwiki
prefix (such as "m:" for meta or "de:" for German), followed
by an optional namespace, followed by the remainder of the
title. Both interwiki prefixes and namespace prefixes have
the same rules: they contain only letters, digits, space, and
underscore, must start with a letter, are case insensitive,
and spaces and underscores are interchangeable.  Prefixes end
with a ":". A prefix is only recognized if it is one of those
specifically allowed by the software. For example, "de:name"
is a link to the article "name" in the German Wikipedia, because
"de" is recognized as one of the allowable interwikis. The
title "talk:name" is a link to the article "name" in the "talk"
namespace of the current wiki, because "talk" is a recognized
namespace. Both may be present, and if so, the interwiki must
come first, for example, "m:talk:name". If a title begins with
a colon as its first character, no prefixes are scanned for,
and the colon is just removed. Note that because of these
rules, it is possible to have articles with colons in their
names. "E. Coli 0157:H7" is a valid title, as is "2001: A Space
Odyssey", because "E. Coli 0157" and "2001" are not valid
interwikis or namespaces.

It is not possible to have an article whose bare name includes
a namespace or interwiki prefix.

An initial colon in a title listed in wiki text may however
suppress special handling for interlanguage links, image links,
and category links.

Character mapping rules: Once prefixes have been stripped, the
rest of the title processed this way: spaces and underscores are
treated as equivalent and each is converted to the other in the
appropriate context (underscore in URL and database keys, spaces
in plain text). "Extended" characters in the 0x80..0xFF range
are allowed in all places, and are valid characters. They are
encoded in URLs.  Other characters may be ASCII letters, digits,
hyphen, comma, period, apostrophe, parentheses, and colon. No
other ASCII characters are allowed, and will be deleted if found
(they will probably cause a browser to misinterpret the URL).
Extended characters are _not_ urlencoded when used as text or
database keys.

Character encoding rules: TODO

Canonical forms: the canonical form of a title will always be
returned by the object. In this form, the first (and only the
first) character of the namespace and title will be uppercased;
the rest of the namespace will be lowercased, while the title
will be left as is. The text form will use spaces, the URL and
DBkey forms will use underscores. Interwiki prefixes are all
lowercase. The namespace will use underscores when returned
alone; it will use spaces only when attached to the text title.

getArticleID() needs some explanation: for "internal" articles,
it should return the "page_id" field if the article exists, else
it returns 0. For all external articles it returns 0. All of
the IDs for all instances of Title created during a request are
cached, so they can be looked up quickly while rendering wiki
text with lots of internal links.
