Editing Character encodings in HTML (section)

==Character references==
{{Main|List of XML and HTML character entity references|Numeric character reference}}

In addition to native character encodings, characters can also be encoded as ''character references'', which can be ''numeric character references'' ([[decimal]] or [[hexadecimal]]) or ''character entity references''. Character entity references are also sometimes referred to as ''named entities'', or ''HTML entities'' for HTML. HTML's usage of character references derives from [[SGML]].

===HTML character references===
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A ''[[numeric character reference]]'' in HTML refers to a character by its [[Universal Character Set]]/[[Unicode]] ''[[code point]]'', and uses the format

{{block indent|<code>&#''nnnn'';</code>}}
or
{{block indent|<code>&#x''hhhh'';</code>}}

where ''nnnn'' is the code point in [[decimal]] form, and ''hhhh'' is the code point in [[hexadecimal]] form. The ''x'' must be lowercase in XML documents. The ''nnnn'' or ''hhhh'' may be any number of digits and may include leading zeros. The ''hhhh'' may mix uppercase and lowercase, though uppercase is the usual style.

Not all [[web browser]]s or [[email client]]s used by receivers of HTML documents, or [[text editor]]s used by authors of HTML documents, will be able to render all HTML characters. Most modern software is able to display most or all of the characters for the user's language, and will draw a box or other clear indicator for characters they cannot render.

For codes from 0 to 127, the original 7-bit [[ASCII]] standard set, most of these characters can be used without a character reference. Codes from 160 to 255 can all be created using [[List of XML and HTML character entity references|character entity names]]. Only a few higher-numbered codes can be created using entity names, but all can be created by decimal number character reference.

[[List of XML and HTML character entity references|Character entity references]] can also have the format <code>&amp;''name'';</code> where ''name'' is a case-sensitive alphanumeric string. For example, "λ" can also be encoded as <code>&amp;lambda;</code> in an HTML document. The character entity references <code>&amp;lt;</code>, <code>&amp;gt;</code>, <code>&amp;quot;</code> and <code>&amp;amp;</code> are predefined in HTML and SGML, because <code>&lt;</code>, <code>&gt;</code>, <code>"</code>  and <code>&amp;</code> are already used to delimit markup. This notably did not include XML's <code>&amp;apos;</code> (') entity prior to [[HTML5]]. For a list of all named HTML character entity references along with the versions in which they were introduced, see [[List of XML and HTML character entity references]].

Unnecessary use of HTML character references may significantly reduce HTML readability. If the character encoding for a web page is chosen appropriately, then HTML character references are usually only required for markup delimiting characters as mentioned above, and for a few special characters (or none at all if a native [[Unicode]] encoding like [[UTF-8]] is used). Incorrect HTML entity escaping may also open up security vulnerabilities for injection attacks such as [[cross-site scripting]]. If HTML attributes are left unquoted, certain characters, most importantly [[whitespace character|whitespace]], such as space and tab, must be escaped using entities. Other languages related to HTML have their own methods of escaping characters.

===XML character references===
Unlike traditional HTML with its large range of character entity references, in [[XML]] there are only five predefined character entity references. These are used to escape characters that are markup sensitive in certain contexts:<ref>{{cite book |chapter-url=http://www.w3.org/TR/REC-xml/#sec-references |chapter=Character and Entity References |title=XML |first1=T. |last1=Bray |author-link1=Tim Bray |first2=J. |last2=Paoli |first3=C. |last3=Sperberg-McQueen |author-link3=Michael Sperberg-McQueen |first4=E. |last4=Maler |first5=F. |last5=Yergeau |publisher=[[W3C]] |date=26 November 2008 |access-date=8 March 2010}}</ref>

{| class="wikitable"
! Reference !! Character !! Name !! Code point
|-
| <code>&amp;amp;</code>  ||align="center"| & || [[ampersand]]     || U+0026
|-
| <code>&amp;lt;</code>   ||align="center"| < || less-than sign    || U+003C
|-
| <code>&amp;gt;</code>   ||align="center"| > || greater-than sign || U+003E
|-
| <code>&amp;quot;</code> ||align="center"| " || quotation mark    || U+0022
|-
| <code>&amp;apos;</code> ||align="center"| ' || apostrophe        || U+0027
|}

All other character entity references have to be defined before they can be used. For example, use of <code>&amp;eacute;</code> (which gives é, Latin lower-case E with acute accent, U+00E9 in Unicode) in an XML document will generate an error unless the entity has already been defined. XML also requires that the <code>x</code> in hexadecimal numeric references be in lowercase: for example <code>&amp;#xA1b</code> rather than <code>&amp;#XA1b</code>. [[XHTML]], which is an XML application, supports the HTML entity set, along with XML's predefined entities.