'Yay' as a pronoun or adjective

'Yay' as a pronoun or adjective
 

I was watching the season finale of The Good Wife and in one scene -I'm not giving details to avoid spoilers- some character is accused of sending an anonymous envelope because somebody in the post office recognized his photo. He replies:

-I have a niece and I sent her a University of Michigan T-shirt in an envelope, and that envelope was about... (handling the anonymous envelope) ... hmm! ... (in a slightly snide, mocking tone) ... it was about yay big.

I suppose there's something subtle in that yay and my first intuition was thinking in our "¡mirá vos!" or a most general "hete aquí" meaning something like "what a coincidence! strange world!".

May somebody explain it, please?

Yay in this case means that.
It is often accompanied by a gesture giving the approximation of the size.

Está así largo
is how you may say it in Spanish.

I would translate it as "era así de largo" (demonstrating size by gesture).

http://en.wiktionary.org/wiki/yea (adverb, 2).

(Modifica un adjetivo, por lo cual es adverbio).

Thank to both of you. Then, in "yay big" there's no additional nuance over just saying "this big" or "that big", or is there some?.

The Spanish equivalent is "un sobre (más o menos [=about]) así de grande" or "un sobre (como [=about]) de este tamaño" and the nuance I perceived would be carried by pronouncing "así" or "este" in an ascending intonation and in a strong manner, pretty much as "¡así!"

There's no additional nuance provided by using "yay" like this; it's rather neutral.

Gracias por eso

¡Excelente! Muchas gracias a los tres.

IMO it's more informal.