A caret ^ in Regular Expression is usually used to denote the beginning of a line. However, a caret placed inside square brackets can also serve another purpose. The caret comes before characters that you do not want to be included in your search results. For example this search: [^A-z\s]
. . . finds all non-letters and non-space characters (anything that is not a tab , line return, blank space, etc.).
Change the search to: [^0-9\s]
. . . and all letters will be returned.