[Groff] mm EQN?

[Janez Žemva]

The man pan on EQ says:
EQ [label]
Equation start.  EQ/EN are the delimiters for equations  written
for  eqn.   EQ/EN must be inside a DS/DE-pair, except when EQ is
only used to set options in eqn.  The label will appear  at  the
right  margin  of  the equation, unless number register Eq is 1.
Then the label will appear at the left margin.

Does this mean I need to use .EQ with the following prologue?
.DS I
.EQ blah blah
.EN
.DE

Or have I misunderstood something?