public void addFocusListener(FocusListener listener) {
		linker.addFocusListener(listener);
		assembly.addFocusListener(listener);
	}
Add a focus listener to the box(es)

<p>
<b>NOTE:</b> The listener will not fire when focus passes among the linked boxes of the dual
variant.

@param listener the listener
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/assembler/AssemblyDualTextField.java