Propagation on tangent edge:
When you select the reference edge of a face, you can propagate or not the draft on the tangent edges.

For example, if you select the red edge of the above shape, 2 cases are possibles:
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In the case you do propagate on tangent edges, all the tangent edges are fix. |
In the case you do not propagate, only the selected edge is fix. |
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The draft resulting is made of several faces (depending on the number of reference edges). The part above the selected edge does not overflow in the initial shape. |
Here, the result of the facing is a single face. The part above the selected edge overflows in the initial shape. |