[Editorial note: parent and self are reserved class names. Functions and constants with their names can be declared, but not userspace classes]
true, false and null are not listed because they are globally-defined constants, not reserved words.
No idea about parent or self, though.
List of Reserved Words
Table of Contents
The following is a listing of predefined identifiers in PHP. None of the identifiers listed here should be used as identifiers in any of your scripts unless explicitly noted otherwise. These lists include keywords and predefined variables, constant, and class names. These lists are neither exhaustive nor complete.
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