Markup tags can be used in pairs, such as
..., or they can be singular. A single tag is called an empty tag because no content
is included. Single tags in XML must include an ending slash??”as in
, for example??”and
are used to mark where something occurs. Here,
indicates that no sales tax is to be applied to
this invoice.
Also like HTML, XML tags can include attributes and values. As with HTML, XML attributes further
describe the tag, much like an adjective describes a noun. For example, another way to write the
tag is as follows:
With a more generalized tag such as this one, you can easily change values, as in To???>, rather than include another new tag.
In all, XML recognizes six kinds of markup:
n Elements: Elements are more commonly known as tags and, as in HTML, are delimited by a set
of angle brackets <>. As noted previously, elements can also have attributes set to particular values.
Although surrounding values with quotes is optional in HTML??”such as in color=white??”
quotes are mandatory in XML.
n Entity references: Certain characters in XML, such as the delimiting angle brackets, are reserved
in order to permit markup to be recognized.
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