How do I select multiple elements for a query atom in a WebCSD substructure search?

To create a query that includes an atom that can be one of multiple elements, you start by clicking the periodic table icon if the periodic table is not visible. You can select the elements you want to allow by shift-clicking them in the periodic table. When you click on the canvas to place the atom it will be displayed as QA and hovering over it will display the list of allowed elements. You can also click on an existing atom to change it to allow multiple elements, or replace the multiple elements by a single element by selecting just one element in the periodic table or the list of common elements before clicking on the atom. If your search includes more than one combination of elements they will be displayed as QA, QB and so on - again, hovering over an atom will show what elements are allowed.