class_docstr: A reference frame in classical mechanics.
  
  ReferenceFrame is a class used to represent a reference frame in classical
  mechanics. It has a standard basis of three unit vectors in the frame's
  x, y, and z directions.
  
  It also can have a rotation relative to a parent frame; this rotation is
  defined by a direction cosine matrix relating this frame's basis vectors to
  the parent frame's basis vectors.  It can also have an angular velocity
  vector, defined in another frame.
docstr: The basis Vector for the ReferenceFrame, in the x direction. 
docstr_tok: ["The","basis","Vector","for","the","ReferenceFrame",",","in","the","x","direction","."]
code: def x(self):
      """The basis Vector for the ReferenceFrame, in the x direction."""
      return self._x
  
imports: from sympy import diff, expand, sin, cos, sympify, eye, zeros, ImmutableMatrix, MatrixBase
  from sympy.core.symbol import Symbol
  from sympy.simplify.trigsimp import trigsimp
  from sympy.physics.vector.vector import Vector, _check_vector
  from sympy.utilities.misc import translate
  from warnings import warn
label_desc: Use image node_id 24 for calling the ReferenceFrame obj's underlying member method code with example usage: obj.x() and returns: self