XmStringConcat copies s2 to the end of s1 and returns
a copy of the
resulting compound string. The original strings are preserved. The space
for the resulting compound string is allocated within the function. After
using this function, free this space by calling XmStringFree.
s1
Specifies the compound string to which a copy of s2 is appended
s2
Specifies the compound string that is appended to the end of s1