| Feature | modified_base |
| Definition | the indicated nucleotide is a modified nucleotide and should be substituted for by the indicated molecule (given in the mod_base qualifier value) |
| Optional Qualifiers |
/allele="free text" /frequency="free text" representing the proportion of a population carrying the feature expressed as a fraction /gene="free text" /gene_synonym="free text" /map="free text" /note="free text" |
| Comment | value for the mandatory mod_base qualifier is limited to the restricted vocabulary for modified base abbreviations in paragraph 2 of this Annex. |