Every element in FancyMenu has a unique identifier that gets automatically applied to it when creating it.
These identifiers are used to, well, identify the element, so other parts of FancyMenu, like placeholders, actions and loading requirements can communicate with the element.
To get the identifier of an element, because you need it somewhere else, just right-click the element in the editor and click on Copy Element Identifier. Doing that will copy the element's identifier to the clipboard, so you can easily paste it where you need it.