Composting for Flowerbeds

Hi. I came across this on a website recently and wondered if anyone could clarify what it means:
"Help your new plants and flowers bloom by digging a 10cm layer of compost into the soil prior to planting."

Does this mean you must literally dig a 10cm trench where the plants will go, apply the compost, and cover with soil? Or that scatter compost around the flowerbed and ensure it reaches 10cm high? Or does the 10cm apply to the width of the mix?
I would like to know how to compost and whether or not one should best cover the planting area in it, or pour it all on and turn the soil, or else actually dig the soil up and refill with compost.

 

Its a 10cm deep layer on top of the bed, and then you work it in (or let the worms do it if the soil is already in good heart)

Mixing compost with the soil that you then use in the planting-hole should work too - more localised to where the plant is growing, but doesn't help when the plant roots grow outside the original planting-hole

 

Thanks for that, Kristen, I appreciate your answer.