title: pyparsing.ParseException when using parseString (searchString works)
body: <p>I'm trying to parse some Traffic Violation sentences using pyparsing, when I use <code>grammar.searchString(sentence)</code> it is ok, but when I use <code>parseString</code> a <code>ParseException</code>   is thrown. Can anybody help me please saying what is wrong with my code?</p>
  
  <pre><code>from pyparsing import Or, Literal, oneOf, OneOrMore, nums, alphas, Regex, Word, \
      SkipTo, LineEnd, originalTextFor, Optional, ZeroOrMore, Keyword, Group
  import pyparsing as pp
  
  from nltk.tag import pos_tag
  
  sentences = ['Failure to control vehicle speed on highway to avoid collision','Failure to stop at stop sign', 'Introducing additives into special fuel by unauthorized person and contrary to regulations', 'driver fail to stop at yield sign at nearest pointf approaching traffic view when req. for safety', 'Operating unregistered motor vehicle on highway', 'Exceeding maximum speed: 39 MPH in a posted 30 MPH zone']
  
  
  for sentence in sentences:
      words = pos_tag(sentence.split())
      #print words
      verbs = [word for word, pos in words if pos in ['VB','VBD','VBG']]
      nouns = [word for word, pos in words if pos == 'NN']
      adjectives = [word for word, pos in words if pos == 'JJ']
  
      adjectives.append('great')  # initializing  
      verbs.append('get') # initializing 
  
  
      object_generator = oneOf('for to')
      location_generator = oneOf('at in into on onto over within')
      speed_generator = oneOf('MPH KM/H')
  
      noun = oneOf(nouns)
      adjective = oneOf(adjectives)
  
      location = location_generator + pp.Group(Optional(adjective) + noun)
  
      action = oneOf(verbs)
      speed = Word(nums) + speed_generator
  
      grammar =  action | location | speed
  
      parsed = grammar.parseString(sentence)
  
      print parsed
  </code></pre>
  
  <p>Error traceback</p>
  
  <blockquote>
    <p>Traceback (most recent call last): File "script3.py", line 35, in  parsed = grammar.parseString(sentence) File "/Users/alana/anaconda/lib/python2.7/site-packages/pyparsing‌​.py", line 1032, in parseString raise exc pyparsing.ParseException: Expected Re:('control|avoid|get') (at char 0), (line:1, col:1)</p>
  </blockquote>