A file-format is the specific way of ordering and grouping of information in a (computer) file.
File-formats can explicitly defined in standards or documentation, or implicitly defined by acceptability to some processing program.
File-formats of explicitly defined standards can often evolve based on version numbers.
For ease of recognition file formats often have a unique sequence of first few bytes (the header). File-formats like EPUB, which start with the header of the ZIP container format the are build upon, have such recognisable 'header' in the first file in the container (called
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