Saxon supports the full XSLT syntax for patterns. The rules below describe
a simplified form of this syntax (for example, it omits the legal but useless pattern
pattern ::= path ( '|' path )*
path ::= anchor? remainder? (Note 1)
anchor ::= '/' | '//' | id | key
id ::= 'id' '(' value ')'
key ::= 'key' '(' literal ',' value ')'
value ::= literal | variable-reference
remainder ::= path-part ( sep path-part )*
sep ::= '/' | '//'
path-part ::= node-match predicate+
node-match ::= kind-match | type-match
kind-match ::= element-match |
element-match ::= 'child::'? ( name | '*' )
text-match ::= 'text' '(' ')'
attribute-match ::= ('attribute::' | '@') ( name | '*' )
pi-match ::= 'processing-instruction' '(' literal? ')'
any-node-match ::= 'node' '(' ')'
type-match ::= ('element'|'attribute')
'(' ('*'|node-name) (',' type-name) ')'
predicate ::= '[' ( boolean-expression |
numeric-expression ) ']'
Note 1: not all combinations are allowed.
If the anchor is '//' then the remainder is mandatory.
The form of a literal is as defined in expressions; and a predicate is itself a boolean
or numeric expression. As with predicates in expressions, a numeric predicate [P] is shorthand
for the boolean predicate [position()=P].
Informally, a pattern consists of either a single path or a sequence of paths separated
by vertical bars. An element matches the match-pattern if it matches any one of the paths.
A path consists of a sequence of path-parts separated by either "/" or "//".
There is an optional separator ("/" or "//") at the start; a "//" has no effect and
can be ignored. The last path-part may be an element-match, a text-match, an
attribute-match, a pi-match, or a node-match; in practice, a path-part other than the last
should be an element-match.
The axis syntax child:: and attribute:: may also be used in patterns, as described in the XSLT