Using Flash Builder 4, you can collapse all function definitions in the current source file by doing the following:
1) In the left margin of the source pane, where it shows the line numbers of your code, right-click.
2) From the popup menu, select "Folding".
3) From the submenu that appears, select "Collapse Functions".
I know that, but there is in fact a specification : it works only with AS files, but not with as code in MXML files.