oid_xpath_boolean
oid_xpath_boolean (oid, expr[, nsOid])
This function evaluates an XPath expression in the context of an OID and returns 1 (true) if expr is true, otherwise it returns 0 (false).
• oid — The object to use as the context node.
• 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()
• nsOid (optional) — The node used for resolving namespace prefixes in the XPath expression.
The nsOid parameter is useful when you need to evaluate the same XPath expression against many XML documents. Those documents might use a different namespace prefix than the XPath expression. If you provide an OID where the namespace prefix is declared, its URI can be matched up with the document instances regardless of the namespace prefixes they used. For example, you might have a configuration file that uses XPath expressions to specify naming rules with namespace prefixes declared on its root element.
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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