You have to prefix the pieces in the promoChoice string with an asterisk, and include the line holdingsType=1 in the diagram description, to tell the diagram it should collect captured pieces in the holdings. I see the HTML code generated by the Applet does not automatically include that line when the promoChoice contains an asterisk; I will correct that.
Promotion to captured pieces only unfortunately does not work in the Applet, because the holdings are already stuffed with 99 pieces of each type, so you can drop those on the board for setting up the initial position. So it thinks there are always enough pieces available to promote to.
You have to prefix the pieces in the promoChoice string with an asterisk, and include the line holdingsType=1 in the diagram description, to tell the diagram it should collect captured pieces in the holdings. I see the HTML code generated by the Applet does not automatically include that line when the promoChoice contains an asterisk; I will correct that.
Promotion to captured pieces only unfortunately does not work in the Applet, because the holdings are already stuffed with 99 pieces of each type, so you can drop those on the board for setting up the initial position. So it thinks there are always enough pieces available to promote to.