AEIO_InitOutputSpec

I am trying to write an output plugin based on the FBIO example and I am confused about how to set the proper output options.  When the sample code initializes the output spec it uses a pseudo file header and sets the size of the options handle to the size of this pseudo file header structure.  Are the fields of this header also a definition of what is necessary for a proper output spec?  Do I set them only by using the AEGPIOOutSuit4 functions?  The sample code also seems to treat this information as options which are just for this output format and stored separately from the spec in a "disk-safe copy of your options data."

I gather AEIO plugins distinguish between "user data" to be embedded in the file (what I would call the file header) and "options" which are information about the file, such as dimensions, compression, etc.  If these are options which can be set when a specific file is written, surely they are also embedded in the file header so that it can be read properly.

I'm obviously not getting something and would appreciate any pointers as to what to read or where to look at more sample code.

Thanks.