[Gdal-dev] input format

[Matt Hanson]

I apologize for bringing up an issue that I know has been covered/answered before, I just can't remember what the answer was!  (and there's no web-based search for the list archives).
 
How does GDAL decide which format to use to open a file?   In some cases there might be multiple methods: such as a raw binary file but also an ENVI header file.  Or in our case, we have an ENVI style aux file, but an ENVI header may also be present.    I suspect it runs through the list of formats and opens it with the first one that works.   Assuming this is so, how can I force opening a file with a specific format?  
 
In the case of ENVI files (and similar formats that use secondary files) it seems that it would make more sense to allow the user to open the hdr file rather then the binary file, because while the binary file format could be ambiguous, the hdr file would not be.
 
thanks, matt