This dialog is displayed when you click 
in the Symbol Font or Symbol Font Character columns in the Layer Theme Editor. It is used to specify which font and character is to be used as a symbol in a selected theme.
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To specify the font and character which is to comprise the symbol:
- Select the Font to be used to display the symbol from the dropdown.
- Select the symbol to be used from the available ones for the selected font in the grid window. The selected symbol is then displayed in the preview pane.
- Click OK to confirm the selection.