[exim] Character escaping / length restrictions in filter fi…

I'm currently developing a pre-parser which creates exim filter files.
It takes input templates like

mail from "%VARFROM%" subject "%VARSUBJ%" text "%VARTEXT%"

and produces output like

mail from "foo@???" subject "On vacation" text "Bla bla bla"

(it simply replaces the key-string %VAR% by the corresponding value).

I wonder

- if I have to impose any restriction on the length of the variables
(e.g. will a %VARTEXT% with a length of 5kb break the exim filter
parser?)

- which characters within the variables need to be escaped (the
alpha-version of the parser just translates newslines to "\n" and
escapes quotation marks).

TIA,
Chris