### Header window

This window lists all the header information.

To edit a keyword entry, single click that keyword using the left mouse button. The entry will be copied into an entry box at the bottom of the window. Make your modifications there and then press <Return> to make the changes.

After selecting a keyword, the right mouse button (Control-Click on MacOS) will bring up a menu for editing. You can insert a new keyword in front of the selected keyword or delete it. An Undo function is also available. These functions are also listed in the Edit menu.

If the highlight for a keyword is brown, you have selected a mandatory keyword and can only edit its comment. You also cannot insert a new keyword within the initial set of mandatory keywords. This keyword protection can be deactivated from the Preferences window. Warning: modifying mandatory keywords can corrupt your FITS file and may cause fv to crash.

The "Search for" entry box allows you to search for strings in the header. Type the string in the entry box and click "Find". Click the "Case sensitive" button to toggle between case sensitive and case insensitive searching mode.

### Menus

- File
  - Save: Save current FITS file. If the current extension has not been modified, this menu item is disabled.
  - Export as Text: The contents of the header will be dumped to an ASCII file.
  - Close: Close the header window.
  If the "Write History Keyword" option is on (see Preferences help), then a HISTORY keyword is added to the file, listing the user name and date, when a modified extension is closed/saved.

- Edit
  - Undo: Undo an action. Unlimited undos are available.
  - Cut: Delete the current keyword and copy it to the clipboard.
  - Copy: Copy the current keyword to the clipboard.
  - Paste: Insert the contents of the clipboard at the current position.
  - Clear: Delete the current keyword and insert a new one.
  - Clipboard: Display the contents of the clipboard.
  - Insert Key: Insert a new keyword before the currently selected one
  - Delete Key: Delete the currently selected keyword
  - Preferences: Open fv's preferences dialog box
- Tools
  - Create Checksum: Create new checksum keywords
  - Verify Checksum: Check the validity of the checksum keywords, if they exist. If incorrect or nonexistant, correct values can be calculated.

  Go to About fv.