In triangle $XYZ$, $\angle XZY = 50^\circ$ and $\angle ZXY = 70^\circ$. Let $H$ be the orthocenter of triangle $XYZ$. If $D$ is the foot of the altitude from $X$ to $YZ$, what is the measure of $\angle YHZ$? Let's think step by step and output the final answer within \boxed{}.
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