The result of over twenty years of research, the Common European Framework of Reference for Languages: Learning, teaching, assessment (CEFR) is exactly what its title says it is: a framework of reference. It was designed to provide a transparent, coherent and comprehensive basis for the elaboration of language syllabuses and curriculum guidelines, the design of teaching and learning materials, and the assessment of foreign language proficiency.
R. Aler, D. Borrajo, and P. Isasi. Proceedings of the 2001 Congress on Evolutionary
Computation CEC2001, page 1220--1227. COEX, World Trade Center, 159 Samseong-dong,
Gangnam-gu, Seoul, Korea, IEEE Press, (27-30 May 2001)