More clear messages when validating integer values

[raducoravu]

Started based on a discussion on the Oxygen XML Users List which contains more details: https://www.oxygenxml.com/pipermail/oxygen-user/2022-September/006869.html

You have this XML:

<?xml-model href="n.rnc" type="application/relax-ng-compact-syntax"?>
<stuff>1.0</stuff>

and this RNC file:

start = stuff
stuff = element stuff { xsd:integer {minInclusive = "1" maxInclusive = "1"}
}

The validation message for this case states:

      character content of element "stuff" invalid; must be a decimal number without any significant digits after the decimal point

but there are no significant digits after the decimal point.

[djbpitt]

The issue with values like "1.0" and "1." is the decimal point, and not the digits after it. The error message for "1." says that an integer is required, but because the error message does not say anything about value space vs lexical space, a user might not understand that it is the lexical expression (specifically, the decimal point) that raises the error here.

In both cases a more helpful error message might be that xsd:integer values cannot include a decimal point.