For example, deletions or Find and Replace operations may erase the end of the region. When you change an outlined region, the outlining may be lost. For example, when you copy a region that is collapsed, the Paste operation will paste the copied text as an expanded region. The Copy, Cut, Paste, and drag-and-drop operations retain outlining information, but not the state of the collapsible region. The Undo and Redo commands on the Edit menu affect these actions. When you do not wish to have outlining displayed, you can use the Stop Outlining command to remove the outline information without disturbing your underlying code. When you work in outlined code, you can expand the sections you want to work on, collapse them when you are done, and then move to other sections.

You can change it in Tools > Options > Environment > Fonts and Colors > Collapsible Region. The default highlighting color may seem rather faint in some color configurations. Regions in the outlining margin are also highlighted when you hover over the margin with the mouse. You can see the contents of a collapsed region as a tooltip when you hover over the collapsed region. To collapse an outlining region, double-click any line in the region on the outlining margin, which appears just to the left of the code. If you are a keyboard user, you can choose Ctrl+ M+ M to collapse and expand.

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