The primary syntactic construct in XPath is the expression. An expression matches the production Expr. XSLT and XPointer specify how the context is determined for XPath expressions used in XSLT and XPointer respectively. Location paths Location paths , the most important construct in XPath, can be expressed using a straightforward but rather verbose syntax. There are also a number of syntactic abbreviations that allow common cases to be expressed concisely.
Every axis has a principal node type.
The following figure explains in a visual way most of the axes. Expressions Parentheses may be used for grouping. An argument is converted to type string as if by calling the string function. An argument is converted to type number as if by calling the number function. An argument is converted to type boolean as if by calling the boolean function.