xpath_boolean
xpath_boolean (expr[, doc])
This function evaluates an XPath expression with respect to a document and returns 1 (true) if expr is true, otherwise it returns 0 (false).
• expr — A valid XPath expression.
Do not use expressions that contain position() or last(). They do not work in this context. Use the preceding-sibling or following-sibling axes instead to achieve the desired results. For example:
◦ count(preceding-sibling::*)=0 will test that the context node is the first child of its parent.
◦ count(preceding-sibling::para)=1 will test that the context node is the second para child of its parent.
◦ count(following-sibling::*)=0 is a viable alternative to position()=last()
• doc — The identifier of the document tree to use as the context node. If omitted or 0, the current document is used.
A typical boolean expression will use one of the XPath boolean operators (=, !=, <, >, >=, <=). For example,
count(sect1)=0
Non-boolean results are converted to boolean using standard XPath rules:
• The numbers zero (0) and NaN (not a number) are converted to false. Other numbers are converted to true.
• Node set expressions returning at least one node are converted to true. Empty node sets are converted to false.
• Strings are converted to true if they contain at least one character (including white space). Empty strings are converted to false.
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Because non-empty strings are converted to true, the string “false” and the expression “string(false())” are both converted to true.
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To handle errors, call this function from within a catch.
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