Clarify that all boxes should be registered about mp4ra.github.io

[dwsinger]

Best practice: registered with a single definition.
Next best practice: contextual parsing (as above, depending on the container)
Next worst practice: contextual parsing based on something else (e.g. if in a track with the XXX handler type or YYYY handler type, where that is far away from the box)
Unacceptable practice: collision with no disambiguation possible.

[dwsinger]

Propose changing this on the home page

The registered code-points include four-character codes (4CCs) used in various ways within these file formats, and ObjectTypeIndication values used in MPEG-4 systems. The four-character codes are divided into various categories, for convenience. The largest category is the box (atom) types. The only box (atom) types which are not normally registered are boxes that are within the sample entry (sample description) for, and specific to, a codec or family of codecs, or that are used in a specific coding system (e.g. boxes used in a specific hint track).

to
The registered code-points include four-character codes (4CCs) used in various ways within these file formats, and ObjectTypeIndication values used in MPEG-4 systems. The four-character codes are divided into various categories, for convenience. The largest category is the box (atom) types.

The current best practice is to register all box (atom) types. Historically, some that were clearly contextual were not registered, notably those

• within the sample entry (sample description) for, and specific to, a codec or family of codecs, or
• that are used in a specific coding system (e.g. boxes used in a specific hint track).