eqn_inline is for an inline equation. Inline equations are often used for short equations where it would not be appropriate to display as a block equation. Block equations should be used for equations of significant length.
eqn_inline is a specialization of ph. It can contain MathML.
+ topic/ph d4p-formatting-d/eqn_inline
<p>A sample equation is <eqn_inline>2 + 2 = 4</eqn_inline>.</p>