This is basically a string expansion capability that permits referencing variables, indexing arrays, conditional replacement of variables, case conversion, substring selection, regular expression matching and replacement, character class replacement, padding strings, repeated expansion in a user controlled loop, support of arithmetic expressions in the loop start, step and end conditions, and recursive expansion.
When using variable expansion characters in a Volume Label Format record, the format should always be enclosed in double quotes (").
For example, ${HOME} will be replaced by your home directory as defined in the environment. If you have defined the variable xxx to be Test, then the reference ${xxx:p/7/Y/r} will right pad the contents of xxx to a length of seven characters filling with the character Y giving YYYTest.