The d4p_eqn_block element is for block equations that will use MathML. If you won't use MathML, then you should consider using eqn_block from the d4p_formattingDomain instead.
Like eqn_block, this is a specialization of p. Processors should not number these elements. If a number is needed, then d4p_display-equation should be used instead.
+ topic/p d4p-math-d/d4p_eqn_block