GFF - The acronym originally stood for Gene Finding Format, but current specifications are using Generic Feature Format. GFF is a line based, tab separated format for storing features and annotations. This makes it simple to read and write.
See for an example of writing a GFF file from a Bio::Seq object.
GFF2 specifications are available at the Sanger web site page for more information. This is sometimes called GFF2.5 and was primarily developed for gene features.
Version 3 page has more info.
http://public.ecolihub.net/cgi-bin/validate_gff3_online/validate_gff3_online
The original WormBase GFF3 validator is currently offline.
mmscl\tsupported_mRNA\tCDS\t40759\t41225\t.\t+\t.\tParent=mmscl
mmscl\tsupported_mRNA\texon\t61468\t61729\t.\t+\t.\tParent=mmMAP_17
mmscl\tsupported_mRNA\texon\t63653\t63768\t.\t+\t.\tParent=mmMAP_17
mmscl\tsupported_mRNA\texon\t65434\t65537\t.\t+\t.\tParent=mmMAP_17
mmscl\tsupported_mRNA\texon\t65983\t66383\t.\t+\t.\tParent=mmMAP_17
mmscl\tRepeatMasker\tRepeat\t55\t115\t378\t-\t.\tTarget=B4;Note="(230) 61";Name="SINE/B4"
mmscl\tRepeatMasker\tRepeat\t160\t304\t1153\t+\t.\tTarget=B1_MM;Note="1 147";Name="SINE/Alu"