Patch #755683: Document that there might be a maximum indentation limit.

Fixes #700827

Doc/ref/ref2.tex

@@ -185,7 +185,9 @@ first backslash determines the indentation.
 
 \strong{Cross-platform compatibility note:} because of the nature of
 text editors on non-UNIX platforms, it is unwise to use a mixture of
-spaces and tabs for the indentation in a single source file.
+spaces and tabs for the indentation in a single source file.  It
+should also be noted that different platforms may explicitly limit the
+maximum indentation level.
 
 A formfeed character may be present at the start of the line; it will
 be ignored for the indentation calculations above.  Formfeed