If there is a convention for labeling the vertices of various quadrilaterals $ABCD$ etc.

For example $ABCD$ is a parallelogram. $E$ is a point on $DC$ extended, such that $D$ and $E$ are on opposite sides of $BC$.

For example $ABCD$ is a parallelogram. $E$ is a point on $DC$ extended, such that $D$ and $E$ are on opposite sides of $BC$.