class_docstr: Corpus reader designed to work with corpus created by IPI PAN.
  See http://korpus.pl/en/ for more details about IPI PAN corpus.
  
  The corpus includes information about text domain, channel and categories.
  You can access possible values using ``domains()``, ``channels()`` and
  ``categories()``. You can use also this metadata to filter files, e.g.:
  ``fileids(channel='prasa')``, ``fileids(categories='publicystyczny')``.
  
  The reader supports methods: words, sents, paras and their tagged versions.
  You can get part of speech instead of full tag by giving "simplify_tags=True"
  parameter, e.g.: ``tagged_sents(simplify_tags=True)``.
  
  Also you can get all tags disambiguated tags specifying parameter
  "one_tag=False", e.g.: ``tagged_paras(one_tag=False)``.
  
  You can get all tags that were assigned by a morphological analyzer specifying
  parameter "disamb_only=False", e.g. ``tagged_words(disamb_only=False)``.
  
  The IPIPAN Corpus contains tags indicating if there is a space between two
  tokens. To add special "no space" markers, you should specify parameter
  "append_no_space=True", e.g. ``tagged_words(append_no_space=True)``.
  As a result in place where there should be no space between two tokens new
  pair ('', 'no-space') will be inserted (for tagged data) and just '' for
  methods without tags.
  
  The corpus reader can also try to append spaces between words. To enable this
  option, specify parameter "append_space=True", e.g. ``words(append_space=True)``.
  As a result either ' ' or (' ', 'space') will be inserted between tokens.
  
  By default, xml entities like &quot; and &amp; are replaced by corresponding
  characters. You can turn off this feature, specifying parameter
  "replace_xmlentities=False", e.g. ``words(replace_xmlentities=False)``.
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code: def channels(self, fileids=None):
      if not fileids:
          fileids = self.fileids()
      return self._parse_header(fileids, "channel")
  
imports: import functools
  from nltk.corpus.reader.api import CorpusReader
  from nltk.corpus.reader.util import StreamBackedCorpusView, concat
label_desc: Use image node_id 2 for calling the IPIPANCorpusReader obj's underlying member method code with example usage: obj.channels(fileids) and returns: self