Where is xml?

$\triangle ABC$ satisfies $AB=AC$ , $\angle BAC=36^{\circ}$ and has circumradius $2$ . Let $D$ be a point on the circumcircle $ABC$ such that $OD||BC$ , where $O$ is the circumcenter. Project $D$ onto $AB,AC$ to obtain $E,F$ , i.e. $DE\perp AB, DF\perp AC$ .

Suppose $H$ is the orthcenter of $ABC$ . Then the area of $\triangle HEF$ can be expressed as $\sqrt {\frac {x+\sqrt {m}}{l}}$ , where $x,m,l$ are positive integers, and $m$ is square-free. Find $xml$