The d4p_eqn_inline element is for inline equations that will use MathML. If you won't use MathML, then you should consider using eqn_inline from the d4p_formattingDomain instead.
Like eqn_inline, this is a specialization of ph. Processors should not number these elements. If a number is needed, then d4p_display-equation should be used instead.
+ topic/ph d4p-math-d/d4p_eqn_inline