Shapechange HD limit question

[Ungvar]

Is the Shapechange spell limited by the caster's HD, or just his caster level (up to 25)?

Only the caster level limit is included in the spell description, but the spell description does make reference to Polymorph, which DOES have a caster HD limit.

[Hirax]

Shapechange's definitive writing is in the Rules Compendium, your CL, capped at 25, is how many hit dice the form can have.


SHAPECHANGE
Transmutation (Polymorph)
Level: Animal 9, druid 9, Limbo 9,
Scalykind 9, sorcerer/wizard 9, wu jen 9
Components: V, S, F
Casting Time: 1 standard action
Range: Personal
Target: You
Duration: 10 min./level (D)
This spell functions like polymorph, except that it enables
you to assume the form of any single nonunique creature (of
any type) from Fine to Colossal size. The assumed form can’t
have more than your caster level in Hit Dice (to a maximum
of 25 HD). Unlike polymorph, this spell allows incorporeal
or gaseous forms to be assumed.
You gain all extraordinary and supernatural abilities of the
assumed form, but you lose your own supernatural abilities.
You also gain the type of the assumed form in place of your
own. The assumed form doesn’t disorient you. Parts of your
body or pieces of equipment that are separated from you don’t
revert to their natural forms.
You can become just about anything you’re familiar with,
changing form up to once each round as a free action. The change
can’t take place during another action. If you use this spell to
create a disguise, you get a +10 bonus on your Disguise check.
Focus: A jade circlet worth at least 1,500 gp, which you must
place on your head when casting