[MichaelGG]

Every appearance of SHOULD/MAY in a spec is just begging for bugs or incompatibility. We'd be better off if those words were banned. Spec writers would be less inclined (hopefully) to come up with all sorts of arbitrary behaviour that might happen and could be maybe handled.

[jacquesm]

Should and may are spec weasel words, in specs there must (hah!) be 'MUST' and 'MUST NOT'. Otherwise a spec is just a piece of rope with a pre-tied noose.