Numeric character reference: Difference between revisions

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{{Short description|Common markup construct used in SGML, XML, and HTML}}

{{one source|date=February 2021}}

A '''numeric character reference''' ('''NCR''') is a common [[markup (computer programming)|markup]] construct used in [[SGML]] and SGML-derived markup languages such as [[HTML]] and [[XML]]. It consists of a short sequence of [[character (computing)|character]]s that, in turn, represents a single character. Since [[SGML|WebSgml]], [[XML]] and [[HTML 4]], the code points of the [[Universal Character Set]] (UCS) of [[Unicode]] are used. NCRs are typically used in order to represent characters that are not [[plain text#Encoding|directly encodable]] in a particular document (for example, because they are international characters that do not fit in the 8-bit [[Character encoding|character set]] being used, or because they have special syntactic meaning in the language). When the document is interpreted by a markup-aware reader, each NCR is treated as if it were the character it represents.

==Examples==

In SGML, HTML, and XML, the following are all valid numeric character references for the Greek capital letter Sigma

{| class="wikitable" border="1"

|+ Numerical character reference of {{unichar|03A3|GREEK CAPITAL LETTER SIGMA}}<br/>(Note that {{hexadecimal|0931}} = 931₁₀)

|-

! [[Unicode#Upluslink|Unicode character]]

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In SGML, HTML, and XML, the following are all valid numeric character references for the Latin capital letter AE

{| class="wikitable" border="1"

|+ Numerical character reference of {{unichar|00C6|Latin capital letter AE}}

|-

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In SGML, HTML, and XML, the following are all valid numeric character references for the Latin small letter sharp s ß

{| class="wikitable" border="1"

|+ Numerical character reference of {{unichar|00DF|Latin small letter sharp s}}

|-

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| U+005A || &amp;#90; || &amp;#x5A; || Z

|-

| U+005B || &amp;#91; || &amp;#x5B; || &#91;[

|-

| U+005C || &amp;#92; || &amp;#x5C; || \

|-

| U+005D || &amp;#93; || &amp;#x5D; || &#93;]

|-

| U+005E || &amp;#94; || &amp;#x5E; || ^

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| U+007A || &amp;#122; || &amp;#x7A; || z

|-

| U+007B || &amp;#123; || &amp;#x7B; || &#123;{

|-

| U+007C || &amp;#124; || &amp;#x7C; || -{{pipe}}

|-

| U+007D || &amp;#125; || &amp;#x7D; || &#125;}

|-

| U+007E || &amp;#126; || &amp;#x7E; || ~

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==Compatibility issues==

In the initial versions of [[SGML]] and [[HTML]], numeric character references were interpreted in relationship to the document character encoding, rather than [[Unicode]]. For Latin-script documents, numeric character references to characters between x80 and x9F in those documents will not be correct against [[Unicode]], and must be recoded. HTML standards prior to [[HTML 4]] only supported only Western Latin script documents: the treatment of character references above #7F may vary between applications and national conventions.

For example, as mentioned above, the correct numeric character reference for the [[Euro sign]] "€" <code>U+20AC</code> when using [[Unicode]] is decimal <code>&amp;#8364;</code> and hexadecimal <code>&amp;#x20AC;</code>. However, if using tools supporting obsolete implementations of HTML, the reference <code>&amp;#128;</code> (Euro sign in the [[Cp1252CP-1252]] code page) or <code>&amp;#164;</code> (Euro sign in [[ISO/IEC 8859-15]] ) may work.

As another example, if some text was created originally using the [[MacRoman]] character set, the [[quotation mark glyphs|left double quotation mark]] {{char|“"}} will be represented with code point xD2. This will not display properly in a system expecting a document encoded as UTF-8, ISO 8859-1, or [[CP1252]]CP-1252, where this code point is occupied by the letter [[Ò]]. The correct numeric character reference for {{char|“"}} in HTML 4 and newer is <code>&amp;#x201C;</code>, because [[Unicode#Upluslink|U+]]201C is its UCS code. In some systems, the [[List of XML and HTML character entity references|named character reference]] <code>&amp;ldquo;</code> may also be available.

==See also==

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==References==

{{Reflist}}

{{Unicode navigation}}