rcc documentation lacks detail and explanation

I would like to see much more documentation on the rcc tool and what it does - e.g. what is the purpose of "pass" vs compression - I don't think that is documented here:
http://doc-snapshot.qt-project.org/qt5-5.4/rcc.html

For the record the documentation misses quite a lot of the following detail from the command prompt:

Usage: rcc [options] inputs
Qt Resource Compiler version 5.4.0

Options:
-?, -h, --help Displays this help.
-v, --version Displays version information.
-o, --output <file> Write output to <file> rather than stdout.
-t, --temp <file> Use temporary <file> for big resources.
--name <name> Create an external initialization function with <name>.
--root <path> Prefix resource access path with root path.
--compress <level> Compress input files by <level>.
--no-compress Disable all compression.
--threshold <level> Threshold to consider compressing files.
--binary Output a binary file for use as a dynamic resource.
--pass <number> Pass number for big resources
--namespace Turn off namespace macros.
--verbose Enable verbose mode.
--list Only list .qrc file entries, do not generate code.
--project Output a resource file containing all files from the
current directory.

Arguments:
inputs Input files (*.qrc).