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Synopsis a follow requirement is a conditional Symbol, constraining the characters that can immediately follow a symbol in the input source text.
Syntax
  1. Symbol >> constraint
  2. Symbol !>> constraint
where a constraint is any character class, a literal or a keyword non-terminal Symbol.
Description Using >>, the parser will not accept the Symbol if it is not immediately followed by the terminal in the input string. If the end of the symbol coincides with end-of-file, the constraint will fail and the symbol will not be accepted.

Using !>>, the parser will not accept the Symbol if it is immediately followed by the terminal in the input string. If the end of the symbol coincides with end-of-file, the constraint will always succeed and the symbol is accepted.
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