Readme file for taxmodels.
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Tax models feature is the way to group taxes and make an easier way to modify
taxes in a single place instead of on each product.

The model is a container of tax rates applicable for a product or group of
products. It contains elements, each element is a tax rate with a name for it.

A product can contain only one model, but each model can contain as many
elements as you need.

For example, cigarettes can contain special tax for tobacco and the other
taxes:

    special tax : 10%
    VAT         : 8%
    state tax   : 3%

    The Model for cigarettes is:
        
        Model name: 'Cigarrets'
        Model id  : 2
        Model elements: 5,6,7

    The elements for the cigarettes-model:
        
        Element id: 5
        Element name: 'VAT'
        Element rate: 8

        Element id: 6
        Element name: 'state tax'
        Element rate: 3

        Element id: 7
        Element name: 'special tax'
        Element rate: 10

So, if the tax laws changes, and -lets say- the state tax rate changes to 10%, you
do not need to modify each product that has the state tax. You only need to change
the rate of the element named 'state tax' to 10% and all your products are updated.

The same when -again, lets say- cigarettes are added with a 'healt tax', you only
need to add the element 'healt tax' and add this element to the 'cigarettes' model.