Typoscript properties in the CONFIG section are usually defined once and at a certain point. But what if you have defined the value of a property at some place and like to add another one later in the parsing process?
A prominent example is config.linkVars. In most cases, it's used to append the global language parameter L to typolinks:
config.linkVars = L
However, if you need to append another value to that property using a basis template or an extension template, you can do this with := addToList():
config.linkVars := addToList(print)
Parsing both properties will have the same result as:
config.linkVars = L, print
List of functions
It's so easy, isn't it? Mind the := operator as a placeholder for the parser to process the function. The "TypoScript Syntax and In-depth Study" docs reveal the following list of functions which can be used here. There's even a hook to use your own functions.
... adds a string before the existing one.
... adds a string after the existing one.
... removes a string from the existing one. str_replace() is used here.
... replaces an existing string with a new one. str_replace() is used here,with the pipe symbol | as a divider.
... appends values to a comma separated list. The list will neither be sorted nor distinct. Multiple values are given as a comma separated list.
... removes values from a comma separated list. Multiple values are given as a comma separated list.