Markup

A document entity

[1]

document

::=

prolog element Misc*

consists of markup, that is start tags , end tags , empty-element tags , entity references , character references , comments , CDATA section delimiters , document type declarations and processing instructions , and finally character data .

References constitute a preprocessor and are used, among other things, to represent special characters; they start with & , the rest of the markup starts with < and must not contain < .

White space

White space consists of spaces, tabs, RETURN and LINEFEED:

[3]

S

::=

(#x20 | #x9 | #xD | #xA)+

Within markup white space is processed; outside of markup it is significant. Theoretically a parser has to produce all content. Only if a parser validates does it have to signal if white space is significant or not — this is supposed to be indicated with the attribute xml:space . It remains unclear, if an empty element contains white space or not.

Line separations should be canonicalized to LINEFEED during recognition.

Names

A Name (identifier) is defined as follows:

[4]

NameChar

::=

Letter | Digit | '.' | '-' | '_' | ':' | CombiningChar | Extender

[5]

Name

::=

(Letter | '_' | ':') (NameChar)*

[6]

Names

::=

Name (S Name)*

Letter , Digit , CombiningChar and Extender are certain ranges in Unicode — they include at least the relevant parts of ASCII. The sequence XML in any spelling at the beginning of names is reserved. The colon is used for name spaces; however, they are not defined as part of XML.

Strings

Markup itself only contains white space and NameChar as well as literal data , i.e., arbitrary strings in single or double quotes:

[10]

AttValue

::=

'"' ([^<&"] | Reference)* '"'| "'" ([^<&'] | Reference)* "'"

[67]

Reference

::=

EntityRef | CharRef

[68]

EntityRef

::=

'&' Name ';'

[66]

CharRef

::=

'&#' [0-9]+ ';' | '&#x' [0-9a-fA-F]+ ';'

These strings cannot contain < & and the respective quote, but they can use references

Comments

Comments can contain arbitrary characters except the sequence -- . They must end with --> :

[15]

Comment

::=

'<!--' ((Char - '-') | ('-' (Char - '-')))* '-->'

Comments cannot be nested and they cannot appear everywhere.

Processing Instructions

PIs are meant for programs processing XML. They can contain everything except ?> :

[16]

PI

::=

'<?' PITarget (S (Char* - (Char* '?>' Char*)))? '?>'

[17]

PITarget

::=

Name - (('X' | 'x') ('M' | 'm') ('L' | 'l'))

Once again, XML in any spelling may not be used for a target — but it is for xml-stylesheet .

CDATA Sections

CDATA is used to include arbitrary text and still remain well-formed :

[18]

CDSect

::=

CDStart CData CDEnd

[19]

CDStart

::=

'<![CDATA['

[20]

CData

::=

(Char* - (Char* ']]>' Char*))

[21]

CDEnd

::=

']]>'

Char cannot contain Reference, i.e., one cannot include the terminating ]]> in CDATA . Therefore, CDATA cannot be nested.