1. Thorén C. (Ed.) Nordic guidelines for computer accessibility (2nd edn). Nordic Cooperation on Disability, 1998. http://trace.wisc.edu/docs/nordic_guidelines/nordic_guidelines.htm.
2. Vanderheiden, G.C. (1994). Application software design guidelines: increasing the accessibility of application software to people with disabilities. http://trace.wisc.edu/docs/software_guidelines/software.htm.
3. AENOR (Spanish Association for Standardization and Certification). UNE EX 139802:1998. Health informatics. Computer applications for people with disabilities. Computer accessibility requirements. Software. 1998 (in Spanish).
4. US Access Board. Section 508 standards. 2000. http://www.section508.gov/index.cfm?fuseAction=stdsdoc.
5. ISO/TS 16071:2003. Ergonomics of human-system interaction -- Guidance on accessibility for human-computer interfaces. ISO Technical Specification. 2003.