empty string acceptable or not?

For built-in primitive and derived types, which types can
have empty string in their lexical space (i.e., or empty
string is a valid value).

Is my summary correct?  How can we tell which group
each data type belongs by reading the specification (e.g.,
finite-length sequence of ...)?

Thx,

-Stanley

empty string - a valid value
   string
   normalizedString
   token
   base64Binary
   hexBinary

empty string - an invalid value (unless nil flag is true)
   duration 
   dateTime
   time
   date
   gYearMonth
   gYear
  gMonthDay
  gDay
  gMonth
  boolean
  float
  double
  anyURI
  QName
  NOTATION
  language
  Name
  NCName
  ID
  IDREF
  IDREFS
  ENTITY
  ENTITIES
  NMTOKEN
  NMTOKENS
  decimal
  integer
  nonPositiveIntegere
  negativeInteger
  long
  int
  short
  byte
  nonNegativeInteger
  unsignedLong
  unsignedInt
  unsignedShort
  unsignedByte
  postiveInteger