This screen shot is several years old but still correct. The number of buttons has increased to 2 rows vs. 1 as shown.
Added buttons are the crucial "collapse" and "expand". Collapse condenses a range of lines into a single visible line. The collapsed lines are still in the file but are not displayed. You can collapse any range, not merely following the constraints of a hierarchy. This is ideal for viewing distant parts of a document close to each other.
As noted, local file storage has been removed, largely because it was terrible as a result of awful browser implementations.