This function returns a compressed version of the input data using the DEFLATE data format, or false if an error is encountered. The optional parameter level can be given as 0 for no compression up to 9 for maximum compression.
For details on the DEFLATE compression algorithm see the document "DEFLATE Compressed Data Format Specification version 1.3" (RFC 1951).
See also gzinflate(), gzcompress(), gzuncompress(), gzencode().