Add Note about xsd:float and xsd:double Limitations

[jmkeil]

What about adding a remark in section The XML Schema Built-in Datatypes to increase the awareness of the limitations of the values spaces of xsd:float andxsd:double (see EasierRDF#82 and https://doi.org/10.1007/978-3-031-06981-9_10)? Something like:

• add in the last column of the table

  (but excluding many decimal numbers like 0.1)

  or

  (but not all decimal numbers)

• somewhere after the table add a NOTE box like:

  The Lexical-to-value mapping of xsd:float andxsd:double performs a rounding of the lexical value to the nearest value representable in IEEE 754-2008 binary floating point representation of the according precission. Therefore, many decimal numbers are not exactly represented by xsd:float andxsd:double. For example, ex:a ex:p "0.1"^^xsd:float. actually represents / D-entails ex:a ex:p "0.100000001490116119384765625"^^xsd:float. Only xsd:decimal can exactly represent arbitrarry decimal numbers.

[hartig]

@jmkeil thanks for the suggestion! I have created PR #44 with this change (using slightly different wording).