Normally, typing a command that is not bound by the incremental search exits the search before executing the command.  Thus, the command operates on the buffer from which you invoked the search.  However, if you customize the variable @code{search-exit-option} to <del>@code{nil},</del> <ins>@code{append},</ins> the characters which you type that are not interpreted by the incremental search are simply appended to the search string.  This is so you could include in the search string control characters, such as @kbd{C-a}, that would normally exit the search and invoke the command bound to them on the buffer.