derivedDataType MtasStringDigitsAlphaUnderscore0to64DT

EcimDerivedString with character class [0-9a-zA-Z_] and length (0..64) constraint.

References from:
MtasGaAnn; VtasGaAnn;
stringMtasStringDigitsAlphaUnderscore0to64DT

Valid values: [0-9a-zA-Z_]{0,64}
  derivedDataType MtasStringDigitsAlphaUnderscore0to64DT