This is an old revision of the document!
Here is general information on Context-free Grammars.
Typically, in a context-free grammar one can have multiple productions of the form
N -> w1 N -> w2 M -> w3 M -> w4 M -> w5
I use the notation that corresponds to Backus-Naur form which collects all right-hand sides correspondig to same left-hand sides and separate the alternatives using the “|” sign:
N ::= w1 | w2 M ::= w3 | w4 | w5