The terminology used throughout this manual to describe the CLIPS syntax is fairly common to computer reference manuals. Plain words or characters, particularly parentheses, are to be typed exactly as they appear. Bolded words or characters, however, represent a verbal description of what is to be entered. Sequences of words enclosed in singleangle brackets (called terms or nonterminal symbols), such as <string>, represent a single entity of the named class of items to be supplied by the user. A nonterminal symbol followed by a *, represents zero or more entities of the named class of items which must be supplied by the user. A nonterminal symbol followed by a +, represents one or more entities of the named class of items which must be supplied by the user. A * or + by itself is to be typed as it appears. Vertical and horizontal ellipsis (three dots arranged respectively vertically and horizontally) are also used between nonterminal symbols to indicate the occurrence of one or more entities. A term enclosed within square brackets, such as [<comment>], is optional (i.e. it may or may not be included). Vertical bars indicate a choice between multiple terms. White spaces (tabs, spaces, carriage returns) are used by CLIPS only as delimiters between terms and are ignored otherwise (unless inside double quotes). The ::= symbol is used to indicate how a nonterminal symbol can be replaced. For example, the following syntax description indicates that a <lexeme> can be replaced with either a <symbol> or a <string>.
<lexeme> ::= <symbol> | <string>
A complete BNF listing for CLIPS constructs along with some commonly
used replacements for nonterminal symbols are listed in appendix
H.