* The main mime type should be the canonical one, use aliases for any
     other widely used forms
   * Where there's a hierarchy in the types, list it via a parent
   * Highly specific magic matches get a high priority
   * General magic matches which could trigger a false-positive need
     a low one
   * The priority for containers normally need to be higher than for
     the things they contain, so they don't accidently get detected

The key is interpreted as a field name for struct literals,
an index for array and slice literals, and a key for map literals.
For map literals, all elements must have a key. It is an error
to specify multiple elements with the same field name or
constant key value. For non-constant map keys, see the section on
<a href="#Order_of_evaluation">evaluation order</a>.
</p>

<p>
For struct literals the following rules apply:

pkg encoding/json, type InvalidUTF8Error //deprecated
pkg encoding/json, type UnmarshalFieldError //deprecated
pkg go/build, const AllowBinary //deprecated
pkg go/doc, type Package struct, Bugs //deprecated
pkg go/importer, func For //deprecated
pkg go/importer, func ForCompiler //deprecated
pkg go/types, func NewInterface //deprecated
pkg go/types, method (*Interface) Embedded //deprecated
pkg image, var ZP //deprecated
pkg image, var ZR //deprecated