column family names

[Toby White]

From the HBase documentation (http://wiki.apache.org/hadoop/Hbase/HbaseArchitecture 
)

'A column name has the form "<family>:<label>" where <family> and  
<label> can be arbitrary byte arrays'

yet in HColumnDescriptor.java:

    for (int i = 0; i < (b.length - 1); i++) {
      if (Character.isLetterOrDigit(b[i]) || b[i] == '_' || b[i] ==  
'.') {
        continue;
      }
      throw new IllegalArgumentException("Illegal character <" + b[i] +
        ">. Family names  can only contain  'word characters' and  
must end" +
        "with a colon: " + Bytes.toString(b));
    }

Presumably the code is the authoritative source here; but why is there  
such a restriction on family names?

Toby