Set the content to show as HTML.
In the converter:
getAsObject: return value;
getAsString: return value.join( '<br/>' );
value is a global variable. In getAsObject, it is the submitted value from the browser. In getAsString, it is the "stored" (in memory or on disk) value.
getAsObject is used when converting query string values from the browser to the data type you want stored.
getAsString is used when converting from stored data to a displayable string.
If the data type is a date, or a number, you might want to format it using some sort of converter. I've made simple helper for formatting dates