The content of a variable can be defined over several lines. The start of the definition domain is marked with #define, the end with #end.
Example:
setvar=ls_first=test
#define ls_second
----------------------------
this is a long variable
with a lot of text
-----------------------------
#end
messagebox=<ls_second>
Output:
----------------------------
this is a long variable
with a lot of text
-----------------------------
In this way you can enter a long text into the source code an assign it to a variable.