Specifies the XML Document Object Model (DOM) node on which the expression specified in the expression attribute is rooted.
The expressionContext attribute is an optional attribute of the errorCondition element.
It contains a relative XPath expression that identifies the XML DOM node (within the context of the matched XML DOM node) on which the expression is rooted and therefore should be evaluated. The default value is "." This is the same as the matched XML DOM node.
The following is an example of the expressionContext attribute as it is used in the errorCondition element: