In GFF3, annotating more than one protein-coding gene (i.e. polycistronic) contained in a eukaryotic mRNA
The GFF3 file format specification doesn't care where annotations are described in the file, although it can make some things easier if the annotations are ordered by the start position:

1   T1  gene    3631    4605    .   +   .   ID=ATNG01010
1   T1  mRNA    3631    4605    .   +   .   ID=ATNG01010.1;Parent=ATNG01010
1   T1  exon    3631    3913    .   +   .   ID=ATNG01010:exon:1;Parent=ATNG01010.1
1   T1  CDS     3750    3904    .   -   0   ID=ATRV01011:CDS:1;Parent=ATRV01011.0
1   T1  CDS     3860    3913    .   +   0   ID=ATNG01010:CDS:1;Parent=ATNG01010.1
1   T1  exon    3996    4276    .   +   .   ID=ATNG01010:exon:2;Parent=ATNG01010.1
1   T1  CDS     3996    4260    .   +   2   ID=ATNG01010:CDS:2;Parent=ATNG01010.1
1   T1  exon    4486    4605    .   +   .   ID=ATNG01010:exon:3;Parent=ATNG01010.1


There are many examples in well-studied genomes of overlapping genes, so the GFF3 format needs to be flexible enough to handle these. Different genes can be encoded across the same region, but on different strands. But different genes can also be encoded on the same strand, sometimes sharing an exon.