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XPath
The grammar for specifying a selector or field is a subset of the XPath grammar. While this article does not go into details regarding this grammar, suffice it to say that selectors specify element types via a '/' delimited path. The field grammar is identical to the selector grammar, with the addition of '@' to prefix an attribute type. Note that the following special sub-expressions:
'.' denotes the current element type (much like a directory path)
'*' denotes "all" element types at a given level, as already demonstrated in the previous example.
'//' denotes all children. Like '*', but recursive. This is unlike directory paths, where '//' normally denotes root.
'@' is a prefix that indicates an attribute type. Only a field (not a selector) may specify an attribute type.
The next table provides a set of paths, descriptions, and corresponding XML as fairly encompassing examples of XPath for selectors and fields:
| XPath |
Description |
Structure |
. |
The current element. |
<current>foo</current> |
Xyz |
The child element xyz of the current element. |
<current> <xyz>foo</xyz> <xyz>bar</xyz> </current> |
abc/xyz |
The xyz child element of the abc child element of the current element. |
<current> <abc> <xyz>foo</xyz> </abc> <abc> <xyz>bar</xyz> </abc> </current> |
.//xyz |
Any xyz descendant element of the current element |
<current> <xyz>foo</xyz> <abc> <xyz>bar</xyz> <abc/> <current> |
*/xyz |
The xyz child of any child of the current element. |
<current> <abc> <xyz>foo</xyz> </abc> <def> <xyz>bar</xyz> </def> </current> |
@attr |
The attr attribute of the current element. |
<current attr="1"/> |
xyz/@attr |
The attr attribute of the xyz child element. |
<current> <xyz @attr="1"> <xyz @attr="2"/> </current> |
.//@attr |
Any attr attribute of any descendant element of the current element. |
<current> <xyz @attr="1"/> <abc @attr="2"> <xyz @attr="3"/> <abc/> <current> |
*/@attr |
The attr attribute of any child of the current element. |
<current> <abc @attr="1"> <def @attr="2"/> </current> |