    tt(DEFINE) directives can be used to define symbols for longer strings.
A tt(DEFINE) directive is constructed as follows:
        verb(    DEFINE name     that what is defined by `name')
    Here,
    itemization(
    it() the tt(name) following tt(DEFINE) is the symbol that may be used in
tt(USE) directives (see below) and tt(commands) (see below). 
    it() tt(DEFINE) symbols can be used in other tt(DEFINE) symbols. However,
it is the responsibility of the policy file's author to make sure that
(indirect) circular definitions are avoided. E.g., after:
        verb(    DEFINE A    ${B}
    DEFINE B    ${A}
    DEFINE C    ${C}

    USE MAILARGS ${A} ${B} ${C})
    tt(MAILARGS) will be expanded to 
        verb(     ${A} ${A} ${C})
    it() The text following tt(DEFINE name) is then inserted literally into
the tt(USE) directive or tt(command).

    Example:
        verb(    DEFINE  SSH         /usr/bin/ssh frank@localhost -q
    DEFINE  EXECSHA1     -xdev -perm /111  -type f -exec /usr/bin/sha1sum {} \;)
    The symbols defined by tt(DEFINE) directives may consist of letters,
digits and the underscore characters (tt(_)).  In the definition of the symbol
any character can be used. However, initial and/or trailing blanks are removed
from definitions.

    To insert a definition into a tt(USE) directive or tt(command) use the form
        verb(    ${name})
    E.g., tt(${EXECSHA1}). Concrete examples are provided below.
    )
