Bar repeats indicate that the musical material in preceding bars must be repeated exactly, but without notating that material again. Bar repeats can comprise groups of one, two, or four bars.
For example, a one-bar repeat indicates that the material in one bar is repeated, meaning every bar in the region repeats the same material. A four-bar repeat indicates that the material in the previous four bars is repeated.
This notation short-hand can make repetitive music easier to read, as performers must only read the repeated phrase once and then simply count how many times they repeat it. Bar repeats can also save horizontal space, as bar repeat symbols are usually narrower than the equivalent fully written-out bars.
In Dorico Pro, bar repeat regions are used to display bar repeats, meaning as many bar repeat symbols as necessary to fill the region are shown automatically.
In Write mode, each region has a handle at the start and end, which you can use to move and lengthen/shorten regions.
By default, bar repeat regions are highlighted with a colored background. As you zoom out, the highlights become more opaque, which is especially useful when viewing full score layouts in galley view. These highlights are considered annotations, are not printed by default, and you can hide/show them.
You can also show adjacent bar repeat regions; for example, if you want to use a two-bar repeat in the first iteration of a phrase, and then a four-bar repeat to indicate the whole phrase is repeated. When two different bar repeat regions are adjacent, they alternate highlight colors to ensure the separate regions are always identifiable.