This package offers improvements over previous parsers.
?is substituted for missing input.
The notion of binding power may be unfamiliar to those accustomed to BNF grammars.
When two consecutive objects are parsed, the first might be the prefix to the second, or the second might be a suffix of the first. Comparing the left and right binding powers of the two objects decides which way to interpret them.
Objects at each level of syntactic grouping have binding powers.
A syntax tree is not built unless the rules explicitly do so. The call graph of grammar rules effectively instantiate the sytnax tree.
The JACAL symbolic math system (http://people.csail.mit.edu/jaffer/JACAL) uses precedence-parse. Its grammar definitions in the file jacal/English.scm can serve as examples of use.
 How do I know this? I parsed 250kbyte of random input (an e-mail file) with a non-trivial grammar utilizing all constructs.