= extensible markup language

W3C standard for document markup

• structural and semantic language / document type

  static documents that don’t do anything:

  not a programming language, network protocol

  not a database but can be stored in databases

• plain-text

  portable data, human-readable, machine-readable

• application-specific, extensible

  no fixed set of tags

  can be extended to different needs

• parsing

  content gets parsed off of document

  must be well-formd / syntactically correct

XML ≠ HTML

• presentation language

• Fixed set of tags with predefined meanings

• not extensible

  only used for web pages

element = tags + content

• content can be empty, consist of text, elements or be mixed

• tags are case-sensitive

<tagName attributeName="attributeValue">

Tags can have multiple attributes

• attribute order is not significant

• attribute names must be unique

XML names = element names, attribute names, construct names

• alphanumeric (but foreign letters allowed)

• must start with letter or underscore

  some constraints for :

• must not start with xml (independent of casing)

• no size limit

content must not contain < , & but can use character references instead)

Mandatory:

Optional:

<!-- comment -->

not element

comment must not contain --

<?target instruction?>

ie. <?xml-stylesheet href="course.css" type="text/css"?>

first thing in the document

not element, not processing instruction

should begin with xml (but optional)

ie. <?xml version="1.0" encoding="ISO-8859-1" standalone="yes"?>