In sheet music I currently read, I notice two distinct ways of rendering the measure number. On some staff line beginnings, it's rendered just as a
- bare number (positioned above the clef)
where on other lines (and sometimes in the middle thereof) it's shown in a
- larger font with a rectangular border around the numbers. See the following example:
All are obviously measure numbers, as they match the actual measure count. I suspect, but am not sure whether the bordered measure numbers have a specific meaning, like the start of a section or similar.
Is there a general consensus on how to write measure numbers, and what meaning such borders should convey?