This schema is a minified version of the full GML XSD (available at http://schemas.opengis.net/gml/3.1.1/base/feature.xsd).
It contains only the GML elements that are considered in LIDO. The reason for shipping a minified XSD version are threefold:
1. some versions of libxml2 (2.7.x and earlier) have problems with schema references depending on other schemas
2. GML provides some Schematron rules to ensure ISO compliance. These interfere with LIDO' Schematron rules by marking lido:gml elements as wrong for not being ISO compliant.
3. the validation is much faster without importing the full GML schema