The environment information in each header line clearly identifies an identifier even if the sequence number is meaningless. The ENVIRONMENTS ONLY and GLOBALENVIRONMENTS ONLY options of the REFERENCE command list the procedures within which an identifier is used. If individual procedures are properly sequenced, then the ENVIRONMENTS and GLOBALENVIRONMENTS options give the procedure names and sequence numbers where the references are located. Because references are sorted first by procedure and then by sequence number, all references within a given procedure are grouped together.

If the source is not properly sequenced, the AT <sequence number> option does not work. The form AT <sequence number> IN <procedure specification> has been provided especially for cases where the specified procedure is sequenced properly and contains nested blocks, procedures that redeclare some of its identifiers, or both.

Environment ranges work regardless of the sequencing of the source. Sequence number ranges produce undefined results if the source is improperly sequenced.

The EXPAND and LIST commands, the TEXT option, and the EXPAND option in the DECLARATIONS command perform binary searches on the SYMBOL file to obtain needed text. Therefore, these constructs work only if the needed text is obtained from the currently loaded symbol file and if that file is properly sequenced.