// lib.string.access
// return the character at position n
+ value_type operator[](size_type n) const { return m_pchData[n]; }
value_type at(size_type n) const
{ wxASSERT_VALID_INDEX( n ); return m_pchData[n]; }
// returns the writable character at position n
+ reference operator[](size_type n) { CopyBeforeWrite(); return m_pchData[n]; }
reference at(size_type n)
{
wxASSERT_VALID_INDEX( n );