The power of the SPL Implementation Guide has come to a great extent from the fact that it has built in validation rules (or "validation procedures"), which are testable formal statements written over the XML content using the Schematron framework. I.e., XPath terms are written that either must produce a result (assert rules) or must not produce a result (report rules). We have been able to write rules that can reach into the depth of the chemical models, such as verifying that amino acid connection points actually reach N atoms that are an amino-group and C-atoms that are in a carboxyl group, same for phosphates, thiophosphates and others, which is supported by a QuInChI implementation, a query extension of InChI that is available for the Schematron (XPath) language. An R-SPL validator is also available at the .