class_docstr: XY Line graph class
docstr: All x values
code: def xvals(self):
      """All x values"""
      return [
          val[0]
          for serie in self.all_series
          for val in serie.values
          if val[0] is not None
      ]
  
file_path: pygal/pygal/graph/xy.py
imports: from functools import reduce
  from pygal.graph.dual import Dual
  from pygal.graph.line import Line
  from pygal.util import cached_property, compose, ident
label_desc: Use image node_id 1 for calling the XY obj's underlying member method code with example usage: obj.xvals() and returns: unknown