Requirements specification and RFC

Many of the people when write requirements specification widely use words such as "SHALL", "SHOULD", "MAY" etc... However usage of this words is chaotic, not well-defined, and such technical writer can't describe why he\she use this word and not another.
It is decreases documentation readability because can be treated incorrectly by one stakeholder, when another can understand it correctly.

So it is critical to have some standard for usage of such words, and there is such a standard in RFC documents. It is RFC 2119 - Key words for use in RFCs to Indicate Requirement Levels.

Hope this info helps you to write more strict requirement documents!