Grab a field from the active display and return as string-- not valid for VT100 screens, which have no attributes.
Data String: points to the buffer where data is to be returned. If the session option EAB is set, remember to allocate this to twice the size of the requested field.
Data Length: number of characters to copy from the source field
PS Position: screen position of any character contained in the field, including the attribute byte, remember it starts with 1, not 0.
Returns
Data String: returned field data--starting with first character after the attribute byte and not exceeding the requested data length. If the EAB option is on, every other character is a CGA attribute...as if this was any value in a server environment!
RetCode: WHLLTRUNCATED: not enough room for the complete field
