15.64.61.13  SUBSTITUTE   - This defines a pair of characters to delimit a
substitution.  Substitutions may not be nested.  You define a string,  and
then  it  will  be included in your text when the name is bracketed by the
substitute pair.  When used with  the  escape  character,  you  can  build
complicated  expressions  and  include  them  in  your  titles in a simple
fashion.  If you need to output the begin substitute character you  should
define a substitution for it.
                                  example
     TD:SET TITLE SUBSTITUTE="{}"
     TD:DEFINE STRING curly "{"
     TD:DEFINE STRING SEASONS "spring,summer,winter,fall"
     TD:TITLE TOP "The seasons are {SEASONS}."
Writes the title:
"The seasons are spring,summer,winter,fall."
     TD:TITLE TOP "A left curly bracket is {curly}"
Writes the title:
"A left curly bracket is {"
     TD:SET TITLE SUBSTITUTE="\\"
     TD:TITLE TOP "The seasons are \SEASONS\."
Writes the title:
"The seasons are spring,summer,winter,fall."
     TD:SET TITLE SUBSTITUTE="\"
     TD:TITLE TOP "The seasons are \SEASONS ."
Writes the title:
"The seasons are spring,summer,winter,fall."
     NOTE:  in this example the trailing substitute char is a blank.