fn:substring-before

Returns the part of $arg1 that precedes the first occurrence of $arg2, taking collations into account.

Signatures

fn:substring-before(
    $arg1 as xs:string?, 
    $arg2 as xs:string?
) as xs:string

fn:substring-before(
    $arg1 as xs:string?, 
    $arg2 as xs:string?, 
    $collation as xs:string
) as xs:string

Properties

The two-argument form of this function is deterministic, context-dependent, and focus-independent. It depends on collations.

The three-argument form of this function is deterministic, context-dependent, and focus-independent. It depends on collations, and static base URI.

Rules

If the value of $arg1 or $arg2 is the empty sequence, or contains only ignorable collation units, it is interpreted as the zero-length string.

If the value of $arg2 is the zero-length string, then the function returns the zero-length string.

If the value of $arg1 does not contain a string that is equal to the value of $arg2, then the function returns the zero-length string.

The collation used by this function is determined according to the rules in Choosing a collation.

The function returns the substring of the value of $arg1 that precedes in the value of $arg1 the first occurrence of a sequence of collation units that provides a minimal match to the collation units of $arg2 according to the collation that is used.

Minimal match is defined in [UTS #10].

Error Conditions

A dynamic error may be raised [ERRFOCH0004] if the specified collation does not support collation units.

Examples

The collation used in these examples, http://example.com/CollationA is a collation in which both "-" and "*" are ignorable collation units.

"Ignorable collation unit" is equivalent to "ignorable collation element" in [UTS #10].

The expression fn:substring-before ( "tattoo", "attoo") returns "t".

The expression fn:substring-before ( "tattoo", "tatto") returns "".

The expression fn:substring-before ((), ()) returns "".

The expression fn:substring-before ( "abcdefghi", "--d-e-", "http://www.w3.org/2013/collation/UCA?lang=en;alternate=blanked;strength=primary") returns "abc".

The expression fn:substring-before ( "abc--d-e-fghi", "--d-e-", "http://www.w3.org/2013/collation/UCA?lang=en;alternate=blanked;strength=primary") returns "abc--".

The expression fn:substring-before ( "a*b*c*d*e*f*g*h*i*", "***cde", "http://www.w3.org/2013/collation/UCA?lang=en;alternate=blanked;strength=primary") returns "a*b*".

The expression fn:substring-before ( "Eureka!", "--***-*---", "http://www.w3.org/2013/collation/UCA?lang=en;alternate=blanked;strength=primary") returns "". (The second argument contains only ignorable collation units and is equivalent to the zero-length string.)