computer science

List of XML and HTML character entity references

List of XML and HTML character entity references is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand List of XML and HTML character entity references rather than just read about it. In short: In SGML, HTML and XML documents, the logical constructs known as character data and attribute values consist of sequences of characters, in which each character can manifest directly (representing itself), or can be represented by a series of characters called a character reference, of which there are two types: a numeric character reference and a character entity reference. This article lists the character entity r…

Key takeaways

List of XML and HTML character entity references belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect List of XML and HTML character entity references to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of List of XML and HTML character entity references from memory before moving on to harder problems.

Reference excerpt

In SGML, HTML and XML documents, the logical constructs known as character data and attribute values consist of sequences of characters, in which each character can manifest directly (representing itself), or can be represented by a series of characters called a character reference, of which there are two types: a numeric character reference and a character entity reference. This article lists the character entity references that are valid in HTML and XML documents.

Character reference overview In HTML and XML, a numeric character reference refers to a character by its Universal Coded Character Set/Unicode code point, and uses the format: &#xhhhh; or &#nnn; where the x must be lowercase in XML documents, hhhh is the code point in hexadecimal form and nnn is the code point in decimal form. The hhhh (or nnn) may be any number of hexadecimal (or decimal) digits and may include leading zeros. The hhhh for hexadecimal digits may mix uppercase and lowercase letters, though uppercase is the usual style. The XML and HTML standards restrict the usable code points to a set of valid values, which is a subset of UCS/Unicode code point values, that excludes all code points assigned to non-characters or to surrogates, and most code points assigned to C0 and C1 controls (with the exception of line separators and tabulations treated as white spaces). By contrast, a character entity reference refers to a sequence of one or more characters by the name of an entity which has the desired characters as its replacement text. The format is: &name; where name is the case-sensitive name of the entity. The semicolon is usually required in the character entity reference, unless marked otherwise in the table below (see ). The entity must either be predefined (built into the markup language), or declared in a Document Type Definition (DTD) by using <!ENTITY name "value">.

Standard public entity sets for characters XML XML specifies five predefined entities needed to support every printable ASCII character: &, <, >, ', and ". The trailing semicolon is mandatory in XML (and XHTML) for these five entities (even if HTML or SGML allows omitting it for some of them, according to their DTD). ISO Entity Sets SGML supplied a comprehensive set of entity declarations for characters widely used in Western technical and reference publishing, for Latin, Greek and Cyrillic scripts. The American Mathematical Society also contributed entities for mathematical characters (see ). HTML Entity Sets Early versions of HTML built in small subsets of these, relating to characters found in three Western 8-bit character sets. MathML Entity Sets The W3C developed a set of entity declarations for MathML characters. XML Entity Sets The W3C MathML Working Group took over maintenance of the ISO public entity sets, combined with the MathML and documents them in XML Entity Definitions for Characters. This set can support the requirements of XHTML, MathML and as an input to future versions of HTML. HTML5 HTML5 adopts the XML entities as named character references, and does not group them into sets. The character reference names originate from XML Entity Definitions for Characters. The HTML5 specification additionally provides mappings from the names to Unicode character sequences using JSON. Numerous other entity sets have been developed for special requirements, and for major and minority scripts. However, the advent of Unicode has largely superseded them.

Formal public identifiers for HTML DTD entities subsets The full formal public identifier and system identifier for the DTD entities subset (where the character entity name is defined) is actually mapped from one of the following three defined named entities:

Formal public identifiers for old ISO entities subsets The ISO entities subsets are old (documented) character subsets, which are given SGML character entity names in ISO 8879 and ISO 9573, and which were used in legacy encodings before the unification within ISO 10646. Their full formal public identifiers are as follows:

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Worked examples

Example 1 — a first encounter with List of XML and HTML character entity references

Start with the simplest possible case. Write down what List of XML and HTML character entity references claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to List of XML and HTML character entity references before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about List of XML and HTML character entity references ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of List of XML and HTML character entity references

In research: List of XML and HTML character entity references appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses List of XML and HTML character entity references in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: List of XML and HTML character entity references is common in secondary-school and first-year university syllabi. It links to neighbouring topics HTML, Lists of computer languages, Unicode, so understanding it makes those chapters shorter.
In everyday life: Look for List of XML and HTML character entity references outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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Frequently asked questions

What is List of XML and HTML character entity references in simple terms?

Why does List of XML and HTML character entity references matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study List of XML and HTML character entity references?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

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