No pleading, motion [except for motion to intervene], or other document shall be filed in any case
by any person who is not a party thereto, unless approved by the court. Absent such an order, the
clerk shall not accept any document tendered by a person who is not a party. Should any such
document be accepted inadvertently or by mistake in the absence of such an order, it may be
stricken by the court on its own motion and without notice.
