const compress/flate.DefaultCompression

4 uses

	compress/flate (current package)
		deflate.go#L18: 	DefaultCompression = -1
		deflate.go#L590: 	case level == DefaultCompression:

	compress/gzip
		gzip.go#L22: 	DefaultCompression = flate.DefaultCompression

	compress/zlib
		writer.go#L22: 	DefaultCompression = flate.DefaultCompression