Inconsistency in thickness of strokes for filled icons

[TaigaYamada]

In the Figma guideline Details 1 point 1, it says:

Icons that can't close should have a thicker stroke by .5 px.

The third point of the same section says:

The stroke shouldn't change when filling in shapes.

Combined, these 2 rules indicate that when an icon contains parts that can be filled and other parts that can't be, the parts that can't be filled should be thickened. The prohibition of mixed techniques only applies to parts that are filled in, as quoted above and as provided in the picture inside of the guideline.

However, the naming of the guideline Details 1 point 3 as "Mixing techniques" is slightly misleading and may lead one to think that when any part is filled in, the rest of the icon should not be thickened.

This potentially ambiguous guideline has affected many, many icons.

Examples of affected, un-thickened icons

• Align Bottom (Filled)

  • 
  • Line at the bottom should be thickened

• Animal Dog (Filled)

  • 
  • Tail should be thickened

Examples of (I believe correctly) thickened icons

• Airplane Take Off (Filled)

  • 
  • Ground plane is correctly thickened

• Camera Switch (Filled)

  • 
  • Arrows are correctly thickened

I usually try to spot all instances of the problem before filing an issue, but this time, a far greater number of icons are affected by the issue than anything I have filed so far. The 4 icons mentioned above are just the tip of the iceberg.

Either way this is settled (unifying the style in thickened or un-thickened), many icons would have to be revised.

However, considering the current guideline, I believe the correct choice is to unify the style in thickened strokes.
This way, consistency within the icon style is preserved too. It would look weird if one filled icon had a different stroke thickness from another filled icon.