Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMATICALLY CORRECT
Very occasionally, it may not be clear whether the word that
follows an adverb is linked with the adverb or with whatever lies on
its other side. For example:
Try as she would, she couldn't get around the maddeningly slow moving
van.
Is the reference here to a moving van that is maddeningly slow
or to a plain old van that's moving maddeningly slowly? If the former
is intended, a hyphen to combine maddeningly with slow would
make it clear which word gets linked with which.
Try as she would, she couldn't get around the maddeningly-slow moving
van.
IN MOST CASES, DO USE A HYPHEN FOR
ADVERBS THAT DO NOT END IN LY
The rules are more complex for adverbs that do not have ly endings,
probably because such words may not be as instantly recognizable
as adverbs. Style guides do not completely agree on how to handle
these situations. Rather than prescribing the way to do it, this section
will simply describe the alternatives.
Authorities agree that in most cases, when a "non-ly" adverb
combines with another word to form a compound adjective modifying
a noun, do link the two with a hyphen.
He handed in a well-written essay.
She stared into the still-glowing embers.
His much-loved pet gerbil was getting old.
It was clearly an ill-advised plan.
A fast-talking salesman cornered them and wouldn't leave.
The cat let out a high-pitched yowl when he accidentally dropped the
cantaloupe on her head.
As before, if the compound follows the noun, omit the hyphen,
unless the compound takes one as part of its proper spelling. Note
that the hyphen is part of the spelling in quite a few of these cases.
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The essay was well written.
The embers were still glowing.
The gerbil was much loved.