class_docstr: Returns the execution size for a given order using a *percentage* of the
  volume in a bar.
  
  This percentage is set with the parameter ``perc``
  
  Params:
  
    - ``perc`` (default: ``100.0``) (valied values: ``0.0 - 100.0``)
  
      Percentage of the volume bar to use to execute an order
code: def __call__(self, order, price, ago):
      # Get the volume and scale it to the requested perc
      maxsize = (order.data.volume[ago] * self.p.perc) // 100
      # Return the maximum possible executed volume
      return min(maxsize, abs(order.executed.remsize))
  
file_path: backtrader/backtrader/fillers.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from backtrader.utils.py3 import MAXINT, with_metaclass
  from backtrader.metabase import MetaParams
label_desc: Use image node_id 1 for calling the FixedBarPerc obj's underlying member method code with example usage: obj.__call__(order, price, ago) and returns: min