SPPTNodeIdentity

The identity of a node in a Shared Packed Parse Forest is composed from:

• a unique rule number,
• a starting position indicating the index of a position in the input text of the parse at which this node starts,
• the length (number of characters) of the input text that is matched by this node

If a grammar is ambiguous, a parse result may contain multiple nodes with the same identity but with different children. An SPPF combines these nodes (to avoid duplication) but supports the alternative lists of children.