How can I specify individual code numbers and a general code number format for a Collection?
Open the Collection

To open a recently accessed Collection, click File → Open Collection. Alternatively, Browse... to a Collection that is being newly accessed.
Display the Code Numbers

To view the Collection files in List view, click the "Show list view" button. To display the file code numbers column, click the menu button and choose Code Number.

Set the Code Number Display Preferences

Alternatively, the Collection Settings dialog can be used to set which columns are displayed next to File Name when the Collection first opens. Click the menu button and select Choose settings for this Collection... .

In the Display Settings tab, under Sequence files tab, DNA Files: and/or RNA Files:, click the Code Number check box.
Specify the Code Number Format

In the Code Numbers tab of the Collection Settings dialog, the default code number format is shown as "A1, A2, ..." . To change the code number format, click Edit...

To add other prefixes, click the "plus" button and then choose the desired options. The updated code number format will be shown in green.
To apply the new code number format, click OK.

The code number format will be updated in the Code Numbers tab.
Choose Code Number Format Warnings

If desired, use the check boxes to show warnings for files with incorrectly formatted or duplicate or missing code numbers. Then click OK.
Enable Automatic Code Number Assignment

To enable automatic assignment of code numbers, either when adding a DNA file using the Add DNA File... button or when importing DNA files using the Import/Export menu, click the check box for "Enter the next code number automatically when adding a DNA file". Click OK.
Verify the Code Number Format

When you exit the Collection Settings dialog, the code number format will be updated. In this example, a warning is shown for duplicate code numbers, which are marked with yellow triangles. If desired, click the Show Details... button to list the files, then click OK.

Edit the Code Numbers

To modify code numbers, open the Description Panel. Enter a unique code number for each file.

If a red warning is present below the Code Number: box, the warning will disappear once the code number is unique.

In this example, the yellow triangles in the list box disappear when the code numbers are unique. Note the asterisk in the Collection list, which is a reminder that the file has unsaved changes.
Save the Changes

To save all of the modified files (and remove any asterisks), click File → Save All. Alternatively, to save an individual file, click the "Save" button.