BBCode

BBCode

Development status	Active
Operating system	Cross-platform
Type	message board
Website	php.net/manual/en/book.bbcode.php

BBCode or Bulletin Board Code is a lightweight markup language used to format posts in many message boards. The available tags are usually indicated by square brackets ([ ]) surrounding a keyword, and they are parsed by the message board system before being translated into a markup language that web browsers understand—usually HTML or XHTML.

BBCode was introduced in 1998 by the messageboard software Ultimate Bulletin Board (UBB) implemented in Perl. In 2000 BBCode was used in phpBB—an internet forum system written in PHP. vBulletin also uses BBCode.

quoted text

or

or

or

or

this would be another way to use the [img]url_img[/img] and must be pre-configured for the forum administrator
(And other emoticons, depending on the variant. Most BBCodes do not enclose emoticons in square brackets, leading to frequent accidental usage)

(Specific image and size vary)

Some message boards do not need the square brackets around the markers, e.g.:

(many variants for li and /li, list types (unordered and ordered, with different bullets or counter formats), etc.)

(some variants for thead, rules, etc.)

BBCode is typically implemented by applying a series of regular expression string-replace operations upon the input. Because regular expressions are limited in analyzing the structure of text input, this has the artifact that any non-hierarchical BBCode input will be transformed into invalid non-hierarchical HTML without error.

Applying traditional parsing techniques is made difficult by ambiguities in the markup, such as in [quote=[b]text[/b][/quote], where the input can either be interpreted as "text" quoted from someone called "[b", or the bolded text "text" surrounded by "[quote=" and "[/quote]", i.e. "[quote=text[/quote]".

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Wikipedia