class_docstr: Processor that lowercases all text 
class_docstr_tok: ["Processor","that","lowercases","all","text"]
code: def process(self, doc):
      doc.text = doc.text.lower()
      for sent in doc.sentences:
          for tok in sent.tokens:
              tok.text = tok.text.lower()
  
          for word in sent.words:
              word.text = word.text.lower()
  
      return doc
  
imports: import pytest
  import stanza
  from stanza.models.common.doc import Document
  from stanza.pipeline.core import PipelineRequirementsException
  from stanza.pipeline.processor import Processor, ProcessorVariant, register_processor, register_processor_variant, ProcessorRegisterException
  from stanza.utils.conll import CoNLL
  from stanza.tests import *
label_desc: Use image node_id 3 for calling the LowercaseProcessor obj's underlying member method code with example usage: obj.process(doc) and returns: doc