updateRenderedFieldValue method
Implementation
void updateRenderedFieldValue(String fieldName) {
var fieldElem = getFieldElementNonTyped(fieldName);
if (fieldElem == null) return;
var value = parseChildElementValue(fieldElem);
var renderedFieldsValues = _renderedFieldsValues ??= <String, dynamic>{};
renderedFieldsValues[fieldName] = value;
}