Displays the formatted contents of an OpenVMS control block that
    begins at the address specified by the expression "location."
    Most blocks include a byte that indicates the block type.

    Associated with each type of block is a set of symbols with a
    common prefix. Each symbol's name describes a field within the
    block, and the value of the symbol represents the offset of the
    field within the block.

    If the block-type byte contains a valid block type (and/or
    subtype), SDA retrieves the symbols associated with that type
    of block (see $DYNDEF) and uses their values to format the block.
    If the block-type byte does not contain a valid block type, you
    must use the /TYPE qualifier to format the block.

    For a given block type, all associated symbols have the following
    form:

    <block type>$<type>_<name>

    where type is one of the following:

    B  Byte
    W  Word
    L  Longword
    Q  Quadword

    A  Address
    C  Constant
    G  Global Longword
    P  Pointer
    R  Structure (variable size)
    T  Counted ASCII string (up to 31 characters)

    If SDA cannot find the symbols associated with the block type
    specified in the block-type byte or by the /TYPE qualifier, it
    issues the following message:

    No <block type> symbols found to format this block

    Use the READ command to obtain additional symbol definitions.