A Container is something other than an expression that can act as the container of an expression.
It is typically an object such as a function, a global variable, or in XSLT a template, or an attribute set.
When free-standing XPath expressions are compiled, the static context for the expression acts as its
Get the granularity of the container. During successive phases of compilation, growing
expression trees are rooted in containers of increasing granularity. The granularity
of the container is used to avoid "repotting" a tree more frequently than is required,
as this requires a complete traversal of the tree which can take a measurable time.
0 for a temporary container created during parsing; 1 for a container
that operates at the level of an XPath expression; 2 for a container at the level
of a global function or template