Ptg represents a syntactic token in a formula. 'PTG' is an acronym for '
parse
thin
g'. Originally, the name referred to the single byte identifier at the start of the token, but in POI,
Ptg encapsulates the whole formula token (initial byte + value data).
Ptgs are logically arranged in a tree representing the structure of the parsed formula. However, in BIFF files
Ptgs are written/read in
Reverse-Polish Notation order. The RPN ordering also simplifies formula evaluation logic, so POI mostly accesses
Ptgs in the same way.
@author andy
@author avik
@author Jason Height (jheight at chariot dot net dot au)