[## Notation
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This type of notation add data from request :class:`context` object to expressions.
notation start with :class:`[##` and end with :class:`##]`.
for example in::

   My Id Is : [##cms.query.id##]

Determine that value of :class:`cms.query.id` must be inject to expression in specific location.
suppose value of :class:`id` key in :class:`query string` is Qam-12. after injection process by context,
result is::

   My Id Is : Qam-12

.. note::

   [## Notation is case insensitive.

If data contain more than one value, values presend in :class:`,` delimiter string of concated values.
for example in::

   Names : [##cms.query.names##]

If :class:`query string` is :class:`names=ali&names=amir`, then result is::

   Names : ali,amir

In expression, we can :class:`OR` data source with :class:`|`. in this case in order from left to right,
if specified deta source not found, engine try to find next data source.
for example in::

   First Question : [##cms.form.quiz1|cms.form.quiz2##]

in above notation, if :class:`quiz1` represent in form data than posted to server, entire notation replace with it.
if quiz1 not presented but class:`quiz2` exist, notation replace with class:`quiz2`.

For :

.. csv-table:: Posted Form Fields
   :header: "Name", "Value"
   :widths: 15, 30

   "quiz1", "what is your name?"

result is::
  
  First Question : what is your name?

For :

.. csv-table:: Posted Form Fields
   :header: "Name", "Value"
   :widths: 15, 30

   "quiz2", "where are you from?"

result is::
  
  First Question : where are you from?

For :

.. csv-table:: Posted Form Fields
   :header: "Name", "Value"
   :widths: 15, 30

   "quiz1", "what is your name?"
   "quiz2", "where are you from?"

result is::
  
  First Question : what is your name?

Also we can set default value at right must item in list of data source in :class:`()`. 
for example in case ::

   First Question : [##cms.form.quiz1|cms.form.quiz2##|(NotSet)]

If nether :class:`quiz1` nor :class:`quiz2` peresent in posted form result is::

   First Question : NotSet