Xpath's are heavily used in all parts of the system and has a significant effect at the runtime behaviour especially for a large amout of xui components and rules. The alternative implementation is approximately 10 times faster as the jaxen implementation but has the disadvantage of a reduced functionality. The alternative engine can only process short syntax xpaths like:
/a/b/c
/*/b
//a
/a//b/*
/a/b[1]/c
/a/b[list]
It's not possible to evaluate conditional xpaths like:
/a/b[./c="a"]
/a/b[position(.)==1]
If a non supported xpath is processed the engine will automatically fall back to the jaxen xpath engine.
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