A combo box form field behaves like a combination of a list box and an entry field. Combo boxes are commonly used for presenting a fixed number of choices to the application end-user from which one can be selected, or the end-user can enter a value that is not a member of the list. They also provide a convenient mechanism for presenting these choices in the form of descriptive text rather than as codes. Combo boxes have an assignable data type and data length. The default members of the list can be defined as a sequence of strings separated by the semi-colon (;) character. The default value for the combo box can also be defined; if this value matches a member of the list, then that list item appears in the entry field component and is also highlighted in the list. The number of visible lines for a combo box defines the number of list members that are exposed. The total number of members in the list can exceed this number of members. The members of a combo box list can also be established under Zim program control by using the FORM SET LIST command. The available combo box styles are "Manual Drop", "Automatic Drop", "Always Dropped", "Drive List", "Directory List" and "File List".
| Manual Drop | A "Manual Drop" combo box exposes the visible number of its list members when it gains the input focus by mouse click. |
| Automatic Drop | An "Automatic Drop" combo box always exposes the visible number of its list members when it gains the input focus by any means. |
| Always Dropped | An "Always Dropped" combo box always has the visible number of its list members exposed. |
| Drive List | A "Drive List" combo box is presented as an "Always Dropped" combo box containing a list of the hard disk drives which are currently available. |
| Directory List | A "Directory List" combo box is presented as an "Always Dropped" combo box containing a list of the file system directories which exist beneath the directory path assigned as the value of the combo box. For example, if the value "C:*" were assigned to the combo box, then the combo box list members consist of the names of the directories underneath the directory "C: |
| File List | A "File List" combo box is presented as an "Always Dropped" combo box containing a list of the files which exist within a specified directory path assigned as the value of the combo box. For example, if the value "C:*" were assigned to the combo box, then the combo box list members consist of the names of the files that exist within the directory "C: |