Transforming groups of nodes

• Optional feature
• Sometimes need to transform groups of nodes together. For example, transform occurrences of the string "ISO" into an entity reference.
• Query can return a set of groups of nodes
• Uses generalized regular expression
• Expressions are composed using ?, +, *, |, sequencing just like normal regular expressions.
• Atomic pattern is any predicate that can be applied to a node, instead of simply a single character or character set
• Search domain is any node-set instead of simple a string
• Transformation specification is applied to group of nodes rather than single node
• Extremely powerful but hard to implement efficiently