Search parameter for region of the reference DNA sequence string. This will refer to part of a locus or part of a gene where search region will be represented in 1-based system. Since the coordinateSystem can either be 0-based or 1-based, this search query will include the result of both coordinateSystem that contains the equivalent segment of the gene or whole genome sequence. For example, a search for sequence can be represented as coordinate=1$lt345$gt123, this means it will search for the Sequence resource on chromosome 1 and with position >123 and <345, where in 1-based system resource, all strings within region 1:124-344 will be revealed, while in 0-based system resource, all strings within region 1:123-344 will be revealed. You may want to check detail about 0-based v.s. 1-based above.