Unable to parse unions in WebGL IDLs

[kvark]

Trying to update khronos API specs in gl-rs, I faced these fragment that webidl wasn't able to parse:

[NoInterfaceObject]
interface WEBGL_multi_draw_instanced_base_vertex_base_instance {
  void multiDrawArraysInstancedBaseInstanceWEBGL(
      GLenum mode,
      Int32array or sequence<GLint> firstsList, GLuint firstsOffset,
      Int32array or sequence<GLint> countsList, GLuint countsOffset,
      Int32array or sequence<GLint> instanceCountsList, GLuint instanceCountsOffset,
      Int32array or sequence<GLint> baseInstancesList, GLuint baseInstancesOffset,
      GLsizei drawCount
  );
  void multiDrawElementsInstancedBaseVertexBaseInstanceWEBGL(
      GLenum mode,
      Int32array or sequence<GLint> countsList, GLuint countsOffset,
      GLenum type,
      Int32array or sequence<GLint> offsetsList, GLuint offsetsOffset,
      Int32array or sequence<GLint> instanceCountsList, GLuint instanceCountsOffset,
      Int32array or sequence<GLint> baseVerticesList, GLuint baseVerticesOffset,
      Int32array or sequence<GLint> baseInstancesList, GLuint baseInstancesOffset,
      GLsizei drawCount
  );
};

Error: UnrecognizedToken { token: (172, Or, 174), expected: [""("", "","", ""..."", "">"", ""Identifier"", ""attribute"", ""callback"", ""const"", ""deleter"", ""dictionary"", ""enum"", ""getter"", ""implements"", ""includes"", ""inherit"", ""interface"", ""iterable"", ""legacycaller"", ""maplike"", ""namespace"", ""partial"", ""required"", ""setlike"", ""setter"", ""static"", ""stringifier"", ""typedef"", ""unrestricted""] }', webgl_generator/utils.rs:82:23