Can anyone tell me the use of search attribute in field tag.

Sample from the documentation is below

<field name="partner_id" search="[]" model="res.partner"/>

Sample from the openerp code is below

 <field name="fields_id" search="[('model','=','res.partner'),('name','=','property_account_receivable')]"/>  # account/demo/account_minimal.xml

 <field model="res.country.state" name="state_id" search="[('code','ilike','ca')]"/> # base/res/res_partner_demo.xml

 <field name="account_debit" search="[('code', 'like', '4540%')]"/> # l10n_be_hr_payroll_account/l10n_be_hr_payroll_account_data.xml

Documentation Explanation is below

The search attribute allows to find the record to associate when you do not know its xml id. You can thus specify a search criteria to find the wanted record. The criteria is a list of tuples of the same form than for the predefined search method. If there are several results, an arbitrary one will be chosen (the first one)

I am having some prob in understanding how all the above works. Can anyone help me out how this needs to be used. Is it possible to give dynamic search values from the global filter. Thanks for your time.