XPath/XQuery analyze-string function


Analyzes a string using a regular expression, returning an XML structure that identifies which parts of the input string matched or failed to match the regular expression, and in the case of matched substrings, which substrings matched each capturing group in the regular expression.


$input as xs:string?,
$pattern as xs:string
) as element(fn:analyze-string-result)
$input as xs:string?,
$pattern as xs:string,
$flags as xs:string
) as element(fn:analyze-string-result)


This function is nondeterministic, context-independent, and focus-independent.


The effect of calling the first version of this function (omitting the argument $flags) is the same as the effect of calling the second version with the $flags argument set to a zero-length string. Flags are defined in .

The $flags argument is interpreted in the same way as for the fn:matches function.

If $input is the empty sequence the function behaves as if $input were the zero-length string. In this situation the result will be an element node with no children.

The function returns an element node whose local name is analyze-string-result. This element and all its descendant elements have the namespace URI http://www.w3.org/2005/xpath-functions. The namespace prefix is implementation-dependent. The children of this element are a sequence of fn:match and fn:non-match elements. This sequence is formed by breaking the $input string into a sequence of strings, returning any substring that matches $pattern as the content of a match element, and any intervening substring as the content of a non-match element.

More specifically, the function starts at the beginning of the input string and attempts to find the first substring that matches the regular expression. If there are several matches, the first match is defined to be the one whose starting position comes first in the string. If several alternatives within the regular expression both match at the same position in the input string, then the match that is chosen is the first alternative that matches. For example, if the input string is The quick brown fox jumps and the regular expression is jump|jumps, then the match that is chosen is jump.

Having found the first match, the instruction proceeds to find the second and subsequent matches by repeating the search, starting at the first character that was not included in the previous match.

The input string is thus partitioned into a sequence of substrings, some of which match the regular expression, others which do not match it. Each substring will contain at least one character. This sequence is represented in the result by the sequence of fn:match and fn:non-match children of the returned element node; the string value of the fn:match or fn:non-match element will be the corresponding substring of $input, and the string value of the returned element node will therefore be the same as $input.

The content of an fn:non-match element is always a single text node.

The content of a fn:match element, however, is in general a sequence of text nodes and fn:group element children. An fn:group element with a nr attribute having the integer value N identifies the substring captured by the Nth parenthesized sub-expression in the regular expression. For each capturing subexpression there will be at most one corresponding fn:group element in each fn:match element in the result.

If the function is called twice with the same arguments, it is implementation-dependent whether the two calls return the same element node or distinct (but deep equal) element nodes. In this respect it is non-deterministic with respect to node identity.

The base URI of the element nodes in the result is implementation-dependent.

A schema is defined for the structure of the returned element: see .

The result of the function will always be such that validation against this schema would succeed. However, it is implementation-defined whether the result is typed or untyped, that is, whether the elements and attributes in the returned tree have type annotations that reflect the result of validating against this schema.


In the following examples, the result document is shown in serialized form, with whitespace between the element nodes. This whitespace is not actually present in the result.

The expression fn:analyze-string("The cat sat on the mat.", "\w+") returns <analyze-string-result xmlns="http://www.w3.org/2005/xpath-functions"> <match>The</match> <non-match> </non-match> <match>cat</match> <non-match> </non-match> <match>sat</match> <non-match> </non-match> <match>on</match> <non-match> </non-match> <match>the</match> <non-match> </non-match> <match>mat</match> <non-match>.</non-match> </analyze-string-result>.

The expression fn:analyze-string("2008-12-03", "^(\d+)\-(\d+)\-(\d+)$") returns <analyze-string-result xmlns="http://www.w3.org/2005/xpath-functions"> <match><group nr="1">2008</group>-<group nr="2" >12</group>-<group nr="3">03</group></match> </analyze-string-result>.

The expression fn:analyze-string("A1,C15,,D24, X50,", "([A-Z])([0-9]+)") returns <analyze-string-result xmlns="http://www.w3.org/2005/xpath-functions"> <match><group nr="1">A</group><group nr="2">1</group></match> <non-match>,</non-match> <match><group nr="1">C</group><group nr="2">15</group></match> <non-match>,,</non-match> <match><group nr="1">D</group><group nr="2">24</group></match> <non-match>, </non-match> <match><group nr="1">X</group><group nr="2">50</group></match> <non-match>,</non-match> </analyze-string-result>.

Error Conditions

A dynamic error is raised if the value of $pattern is invalid according to the rules described in section .

A dynamic error is raised if the value of $flags is invalid according to the rules described in section .

A dynamic error is raised if the supplied $pattern matches a zero-length string, that is, if fn:matches("", $pattern, $flags) returns true.


It is recommended that a processor that implements schema awareness should return typed nodes. The concept of "schema awareness", however, is a matter for host languages to define and is outside the scope of the function library specification.

The declarations and definitions in the schema are not automatically available in the static context of the fn:analyze-string call (or of any other expression). The contents of the static context are host-language defined, and in some host languages are implementation-defined.

The schema defines the outermost element, analyze-string-result, in such a way that mixed content is permitted. In fact the element will only have element nodes (match and non-match) as its children, never text nodes. Although this might have originally been an oversight, defining the analyze-string-result element with mixed="true" allows it to be atomized, which is potentially useful (the atomized value will be the original input string), and the capability has therefore been retained for compatibility with the 3.0 version of this specification.