@Jodo: thank you for your information! The coding system will be very useful for shops that offer the whole range of (all four major) credit cards. As we are going to limit the choice to only two cards I will want to visualize the limitation by a pulldown containing only the accepted credit card types.

@Ryan,
putting the card-types into separate lines in the text area improves the situation dramatically. There remains only one thing to be solved: the <p>...</p>-Tags on the beginning and end of each option-line:

Unfortunately I was not able to find the code implementing the variable_set for