BBCode

BBCode ("Bulletin Board Code") is a lightweight markup language used to format messages in many Internet forum software. It was first introduced in 1998.^[1] The available "tags" of BBCode are usually indicated by square brackets ([ and ]) surrounding a keyword, and are parsed before being translated into HTML.^{[citation needed]}

Tags

Example in HTML/CSS BBCode Output

bolded text^[2],
bolded text or
bolded text [b]bolded text[/b] bolded text

italicized text,
italicized text or
italicized text [i]italicized text[/i] italicized text

<ins>underlined text</ins> or
underlined text [u]underlined text[/u] underlined text

<del>strikethrough text</del> or
strikethrough text [s]strikethrough text[/s] ~~strikethrough text~~

<a href="https://en.wikipedia.org">https://en.wikipedia.org</a>
<a href="https://en.wikipedia.org">English Wikipedia</a> [url]https://en.wikipedia.org[/url]
[url=https://en.wikipedia.org]English Wikipedia[/url] https://en.wikipedia.org
English Wikipedia

<img src="https://upload.wikimedia.org/wikipedia/commons/7/70/Example.png" alt="This is just an example" /> [img alt="This is just an example" ]https://upload.wikimedia.org/wikipedia/commons/7/70/Example.png[/img]

<img src="Smileys/Face-smile.svg" alt=":-)"> :) or [:-)]
This would be another way to use the [img]url_img[/img] and must be pre-configured by the forum administrator.
(This 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.)

<blockquote>quoted text</blockquote>
(Usually implemented in more advanced ways.)

[quote]quoted text[/quote]
[quote="author"]quoted text[/quote]
(including optional author)

Using a Wikipedia template:

quoted text

quoted text
— author

<pre>monospaced text</pre> [code]monospaced text[/code] monospaced text

Large Text or
Smaller Text [style size="30px"]Large Text[/style]
[style size="85"]Smaller Text[/style]
(The unit of measurement varies with each BBCode variant and could represent pixels, points, or relative HTML sizes.) Large Text
Smaller Text

Text in fuchsia or
Text in fuchsia [style color="fuchsia"]Text in fuchsia[/style] or
[style color=#FF00FF]Text in fuchsia[/style] or
[color=#FF00FF]Text in fuchsia[/color]
(Both HTML color names and hexadecimal color values are generally supported, although on some boards, you must omit the # from selecting a hexadecimal color.) Text in fuchsia

<ul>
  <li>Entry A</li>
  <li>Entry B</li>
</ul>

<ol>
  <li>Entry 1</li>
  <li>Entry 2</li>
</ol>

[list]
  [*]Entry A
  [*]Entry B
[/list]

[list=1]
  [*]Entry 1
  [*]Entry 2
[/list]

Some message boards do not need the square brackets around the markers.^[3]

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

Entry A
Entry B

Entry 1
Entry 2

<table>
<tr>
  <td>table cell 1</td>
  <td>table cell 2</td>
</tr>
<tr>
  <td>table cell 3</td>
  <td>table cell 4</td>
</tr>
</table>

[table]
[tr]
  [td]table cell 1[/td]
  [td]table cell 2[/td]
[/tr]
[tr]
  [td]table cell 3[/td]
  [td]table cell 4[/td]
[/tr]
[/table]

(Some variants for thead, rules, etc.)

table cell 1	table cell 2
table cell 3	table cell 4

Source:^[4]

Implementation

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.^{[citation needed]}

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].