AM_CREATE_SYMLINE adds symmetry lines or circles between two elements.
+--------------------<-------------------+
| |
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---->(AM_CREATE_SYMLINE)----+---|first element|---|second element|---+----->
This command has no options. Simply indicate two straight elements to create a
symmetry line between them, or two circular elements (circles or arcs) to create
a symmetry circle between them.
Use this action to add symmetry indicators between lines and circular elements.
Between two circular elements, AM_CREATE_SYMLINE draws a circle with a radius
equal to the mean of the elements' radii and with a center point positioned
equidistant from the elements' centers.
AM_MOD_SYMLINE terminate action