Variation in functional status can be caused by a range of pathologies related to body structure and function, which themselves are related to biologic, genetic and environmental factors.

Legal signature requirements as a condition for the validity of certain acts in common law jurisdictions are typically found in the British Statute of Frauds12 and its versions in other countries.13 With time, courts have tended to interpret the Statute of Frauds liberally, out of recognition that its strict form requirements were conceived against a particular background14 and that strict adherence to its rules might unnecessarily deprive contracts of legal effect.15 Thus, in the last 150 years, common law jurisdictions have seen an evolution of the concept of “signature” from an original emphasis on form to a focus on function.16 Variations on this theme have been considered by the English courts from time to time, ranging from simple modifications such as crosses17 or initials,18 through pseudonyms19 and identifying phrases,20 to printed names,21 signatures by third parties22 and rubber stamps.23 In all these cases the courts have been able to resolve the question as to whether a valid signature was made by drawing an analogy with a manuscript signature.