protected final DocumentProperty createChild(DocumentPropertyComponent documentPropertyComponent, String key) {
        return documentPropertyComponent
            .getConstructor(keyPathEndingWith(key))
            .create(this);
    }
Creates a new child on the specified key with the specified data and 
returns it. This method can be overriden by subclasses to create better
implementations.
<p>
<b>Warning!</b> This method is only intended to be called internally and does
not properly configure created children in the responsive model.

@param documentPropertyComponent  the documentPropertyComponent instance
@param key                        the key to create the child on
@return                           the created child
tool-parent/tool-config/src/main/java/com/speedment/tool/config/AbstractDocumentProperty.java