appears next to the line of code where the bookmark is inserted.
Displays a menu that you can use to create or remove placeholders in the Code window, move to the next or preceding bookmark, or clear all of the bookmarks. Bookmarks mark lines of code so that you can easily return to them at a later time.
When you add a bookmark, a appears next to the line of code where the bookmark is inserted.
Toggle Bookmark
Toggles a bookmark on or off.
Toolbar button: 
Next Bookmark
Moves the insertion point to the next bookmark.
Toolbar button: 
Previous Bookmark
Moves the insertion point to the previous bookmark.
Toolbar button: 
Clear All Bookmarks
Removes all bookmarks.
Toolbar button: 