Information scraped from
https://www.riscosopen.org/content/sales/dde-changes-20-to-21:

  * Added definitions for new AOF flags:
    + Symbol attribute bit 13 is meaningful only for function entry point
      symbols in code areas (or for absolute function entry point symbols).
      It declares that the function not only receives its floating point
      arguments in integer registers, but also returns any floating point
      return value in integer registers. A symbolic reference with this
      attribute cannot be matched by the linker to a symbol definition which
      lacks the attribute.
    + Area attribute bit 31 is valid for both code and data areas, and when
      set, indicates:
      * double-precision floating point data in the area is stored using VFP
        rules (endianness matches the rest of the file) rather than FPA rules
        (most-significant word always stored first).
      * for code areas in little-endian mode, that when functions in the area
        receive double-precision arguments and/or return a double-precision
        value in integer registers or on the stack, that the lower register
        number or lower stack address holds the least significant word
        (little-endian VFP compatibilty mode). Otherwise (big-endian mode or
        FPA compatibility mode), the lower register or lower stack address
        holds the most-significant word.
      An area with this attribute cannot be linked with an area which lacks
      the attribute.

