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:
  
    - ``size`` (default: ``None``)  maximum size to be executed. The actual
      volume of the bar at execution time is also a limit if smaller than the
      size
  
      If the value of this parameter evaluates to False, the entire volume
      of the bar will be used to match the order
code: def __call__(self, order, price, ago):
      size = self.p.size or MAXINT
      return min(
          (order.data.volume[ago], abs(order.executed.remsize), size)
      )
  
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 FixedSize obj's underlying member method code with example usage: obj.__call__(order, price, ago) and returns: min