APICover XML merger should be documented in UG

 java -cp apicover.jar com.sun.tdk.apicover.CMerge

CoverageMerge - SignatureTest version 3.0
Available options are:
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-Files <file> Specify where to find input files
-Write <file> Specify where to place generated file
-Strict Strict merging
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-Version Print version information
-Help Print this text
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All options are case-insensitive.