Improvement : adopt RFC 2119 in term of vocabulary #587
Description
it would be nice to adopt https://www.rfc-editor.org/rfc/rfc2119 ( ie MUST / SHOULD , MAY )
depending on the rules level rather than hard coding this keyword in the "error label"
MUST = level Error
SHOULD = level Warning
MAY = level Info
for instance : the warning
Contact details are incomplete: email must be set
Location: info.contact
could be based on the error level set for the rules Contact details are incomplete: email should be set ( ie warning)