Although Perl will automatically grow strings for you, if you need to
   force Perl to allocate more memory for your SV, you can use the macro

       SvGROW(SV*, STRLEN newlen)

##</code><code>##

  Offsets
    Perl provides the function "sv_chop" to efficiently remove characters
    from the beginning of a string; you give it an SV and a pointer to
    somewhere inside the PV, and it discards everything before the pointer.
    The efficiency comes by means of a little hack: instead of actually
    removing the characters, "sv_chop" sets the flag "OOK" (offset OK) to
    signal to other functions that the offset hack is in effect, and it puts
    the number of bytes chopped off into the IV field of the SV. It then
    moves the PV pointer (called "SvPVX") forward that many bytes, and
    adjusts "SvCUR" and "SvLEN".