I created an ICU DecimalFormat string where the positive sign is the word POSITIVE, and the negative sign is the word NEGATIVE.

Per unit test below, this works in ICU, so long as they are escaped, because "E" is a special character in the ICU pattern language. 

But...  I can find no example of this online for ICU nor DFDL.

All examples are of a sign being just a single character, or a pair of single characters before and after for negative values. 

So my question: Do we intend DFDL to support this full generality, or only single characters for the prefix/suffix regions of the textNumberPattern?

Right now I think Daffodil requires the sign to be a single character, which can be one of the special characters only by quoting it individually. E.g., if I wanted the positive sign to be P and negative sign to be N, then I'd use textNumberPattern:

'P'#0.0#;'N'#0.0#

I don't have to quote the N, but I did just for consistency. 

If we want the full generality, I'd appreciate a realistic motivating example of it.

 * and hence DFDL text number patterns can quote strings, not just individual
 * characters.
 *
 * I found no examples of this anywhere. Everything shows patterns where
 * quotes surround only single characters, or are doubled up for self quoting as in
 * the o''clock example.
 */
@Test def testICUDecimalFormatQuoting_01(): Unit = {
  {
    // Note that E is a pattern special character
    val pattern = "'POSITIVE' #.0###;'NEGATIVE' #.0###"
    val df = new DecimalFormat(pattern)
    val actual = df.format(-6.847)
    assertEquals("NEGATIVE 6.847", actual)

  }

  {
    // here we quote only the E, not the other characters.
    val pattern = "POSITIV'E' #.0###;NEGATIV'E' #.0###"
    val df = new DecimalFormat(pattern)
    val actual = df.format(6.847)
    assertEquals("POSITIVE 6.847", actual)
  }
}