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Pathnames matching an *r suffix denote *r files; all others denote working files. Names are paired as explained in ci(1). Revision numbers use the syntax described in ci(1).
This option is obsolescent, since *r normally uses the preceding $Log$ line's prefix when inserting log lines during checkout (see co(1)). However, older versions of *r use the comment leader instead of the $Log$ line's prefix, so if you plan to access a file with both old and new versions of *r, make sure its comment leader matches its $Log$ line prefix.
At least one explicit option must be given, to ensure compatibility with future planned extensions to the rcs command.
The -ksubst options (except -kkv) generate an *r file that cannot be parsed by *r version 4 or earlier.
Use rcs -Vn to make an *r file acceptable to *r version n by discarding information that would confuse version n.
*r version 5.5 and earlier does not support the -x option, and requires a ,v suffix on an *r pathname.
The separator for revision ranges in the -o option used to be - instead of :, but this leads to confusion when symbolic names contain -. For backwards compatibility rcs -o still supports the old - separator, but it warns about this obsolete use.
Symbolic names need not refer to existing revisions or branches. For example, the -o option does not remove symbolic names for the outdated revisions; you must use -n to remove the names.