-Allowed values are: x86, x86-64, sparc, ppc, s390, s390x, arm, mips, alpha, hppa, ia64.
+Allowed values are: x86, x86-64, sparc, ppc, s390, s390x, arm, mips,
+alpha, hppa, ia64.
+.TP
+.I wordsize
+This is the size of registers on the target architecture, it can be
+either 32 or 64.
+.PP
+The attribute value for both attributes can be a comma-separated list of the allowed
+values. Additionally, the first character may be a
+.I '!'
+to reverse the meaning. An attribute value of "!windows,osx", for example, would mean
+that the entry is considered on all operating systems, except on Windows and OS X.
+No spaces are allowed in any part of the value.