Since Yodl version 2.00 symbols can be manipulated. To add text to an existing
symbol the builtin tt(ADDTOSYMBOL) is available. It expects two parameter
lists: the symbol's name, and the text to add to the symbol.  The symbol must
have been created earlier using DEFINECOUNTER (see section
ref(DEFINECOUNTER)). The macro's second argument is not evaluated while
tt(ADDTOSYMBOL) is processed. Therefore, it is easy to add the text of another
symbol or the expansion of a macro to a symbol value. E.g.,
        verb(
    ADDTOSYMBOL(one)(SYMBOLVALUE(two)XXnl())
        )
    This adds the text of symbol tt(two), followed by a new line, to the
contents of symbol tt(one) only when symbol tt(one) is evaluated, not when 
tt(ADDTOSYMBOL) is evaluated.

    Example:
        verb(
    ADDTOSYMBOL(LOCATION)(this is appended to LOCATION)
        )
