decomposed components with flipping transform have their path direction reversed, possibly causing dropouts if they overlap other components; this option ensures they will get reversed as they are decomposed (similar to what ufo2ft DecomposeComponentsFilter or Glyphs.app does when decomposing flipped components).
Also we allow specific instances of to set skipMissingComponents differently from the class default value, and add an alias to MissingComponentError so one doesn't need to import it explicitly but can the pen's class attribute.
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