src/main/java/com/basistech/tclre/Lex.java
void lexnest(char[] interpolated) {
        assert v.savepattern == null;   /* only one level of nesting */
        v.savepattern = v.pattern;
        v.savenow = v.now;
        v.savestop = v.stop;
        v.savenow = v.now;
        v.pattern = interpolated;
        v.now = 0;
        v.stop = v.pattern.length;
    }
void lexnest(char[] interpolated) {
        assert v.savepattern == null;   /* only one level of nesting */
        v.savepattern = v.pattern;
        v.savenow = v.now;
        v.savestop = v.stop;
        v.savenow = v.now;
        v.pattern = interpolated;
        v.now = 0;
        v.stop = v.pattern.length;
    }
lexnest - "call a subroutine", interpolating string at the lexical level
Note, this is not a very general facility.  There are a number of
implicit assumptions about what sorts of strings can be subroutines.