As we described in the section called “Revisions”, revision numbers in Subversion are pretty straightforward—integers that keep getting larger as you commit more changes to your versioned data. Still, it doesn't take long before you can no longer remember exactly what happened in each and every revision. Fortunately, the typical Subversion workflow doesn't often demand that you supply arbitrary revisions to the Subversion operations you perform. For operations that do require a revision specifier, you generally supply a revision number that you saw in a commit email, in the output of some other Subversion operation, or in some other context that would give meaning to that particular number.
But occasionally, you need to pinpoint a moment in time for which you don't already have a revision number memorized or handy. So besides the integer revision numbers, svn allows as input some additional forms of revision specifiers: revision keywords and revision dates.
The various forms of Subversion revision specifiers can be
mixed and matched when used to specify revision ranges. For
example, you can use
REV1 is a revision keyword
REV2 is a revision number, or
REV1 is a date and
REV2 is a revision keyword, and so
on. The individual revision specifiers are independently
evaluated, so you can put whatever you want on the opposite
sides of that colon.