The function zen_get_products_display_price

I'm studying the function zen_get_products_display_price($products_id)
that is called by the script
includes\templates\my_template\templates\tpl_product_info_display.php. and other.

I've seen that in admin I can choose to show a price with taxes included or not, by setting

DISPLAY_PRICE_WITH_TAX = 'true' or
DISPLAY_PRICE_WITH_TAX = 'false'

but I'm not able to understand how the function
zen_get_products_display_price
detect the above setting and how for this works.

Is there some guru that is able to explain me that?
Thanks - Giovanni

DISPLAY_PRICE_WITH_TAX is a configuration flag, set by using the admin panel... and stored in the database.

admin - configuration - my store - Display Prices with Tax

I know this.
My question is related to the function: I don't understand how the function choose to show the price with taxes or not.
the DISPLAY_PRICE_WITH_TAX is not present in the function.

The tax functions are actually using it that are called by the function zen_get_products_display_price ...

A search on:
DISPLAY_PRICE_WITH_TAX

in the Developers Tool Kit will show you all of the files that are using this setting ...