simple literals in concrete RDF syntaxes

Concepts currently says that simple literals are xsd:string.  Is this the
case for all RDF syntaxes, i.e., are there RDF syntaxes that allow simple
literals that mean integers or decimals or floats.

Concepts currently says that simple literals consist of a lexical form
only.  This appears to permit simple literals not to have enclosing quotes.

Wouldn't it be better to just say, that concrete RDF syntaxes may support
simple literals, which do have an explicit datatype.  The concrete syntax
must provide a mapping from simple literals to either literals or
language-tagged strings as defined in Concepts.  For example, 100 might map
to the literal with lexical form "100" and datatype xsd:integer or "100"
might map to ... or "100"@en might map to ....

peter