Bio::FeatureIO is an iterator subsystem for genomic sequence features. Bio::FeatureIO is a handler module for the formats in the FeatureIO set (eg, Bio::FeatureIO::GFF). It is the officially sanctioned way of getting at the format objects, which most people should use. The Bio::FeatureIO system can be thought of like biological file handles. They are attached to filehandles with smart formatting rules (eg, GFF format, or BED format) and can either read or write feature objects (Bio::SeqFeature objects, or more correctly, Bio::FeatureHolderI implementing objects, of which Bio::SeqFeature is one such object). If you want to know what to do with a Bio::SeqFeatureI object, read Bio::SeqFeatureI. The idea is that you request a stream object for a particular format. All the stream objects have a notion of an internal file that is read from or written to. A particular FeatureIO object instance is configured for either input or output. A specific example of a stream object is the Bio::FeatureIO::gff object. WWW: https://metacpan.org/release/Bio-FeatureIO