Why not just quote the source?

// op.c 765
else if (SvPOK(sv)) {
          /* perl4's way of mixing documentation and code
            (before the invention of POD) was based  a
             trick to mix nroff and perl code. The trick was
             built upon these three nroff macros being used in
             void context. The pink camel has the details in
             the script wrapman near page 319. */
    if (strnEQ(SvPVX(sv), "di", 2) ||
    strnEQ(SvPVX(sv), "ds", 2) ||
    strnEQ(SvPVX(sv), "ig", 2))
        useless = 0;
}
[download]