Tokens of the neutral file language

On the token level, the neutral file is considered as a sequence of tokens. The tokens can be formally defined by a regular set R(G) over the graphical alphabet. Besides, a regular set over the set G is defined as follows  

In the following token definition all sets with only one element are denoted by this element. For example, if X is regular over the alphabet, and the character a is an element of the alphabet, then Xa and (X a) ( or aX and (a 6c X), respectively) denote the set resulting from concatenating an element from X with a (or a with an element from X, respectively). 

It is easy to check that all the sets defined below are regular over the graphical alphabet G, where G is defined above. 

The space character delimits tokens except in strings where it is treated as a significant character. In other words, no token except the string may contain space characters. 

that the present neutral file specification could have been formulated without including a facility for escape sequences. However, if at any time in the future escape sequences are required it is necessary to take this possible extension into account at this time. Otherwise, upward compatibility of the previously written files could not be guaranteed. The consequence of this is that in a string the character sequence I must be expressed by an escape sequence. The standard escape sequence for this is 

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Structure attributes (parameters) of type INTEGER have integers as values. The regular set integer (see Tokens of the neutral file language on page 160) formally defines the set of INTEGER constants. 

The REFERENCE- (REF ONLY-) constants are defined by the regular set name (see "Tokens of the neutral file language" on page 160). 

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