Click either Try again to return to a cleared search form, or your browser's back button to preserve the string you already typed. A No Match message means your search string appeared nowhere in the subcode list. Click Try again and enter another string. A leading space will display subcodes containing words that start with the string rather than just contain it. An empty search string will lead to the full list being displayed.
Case is ignored in searches.
Submitting a longer string isn't the only way to reduce an overabundant result. You can add extra strings, separated by spaces, to narrow the search. Words starting with the extra strings are sought. The order of the strings is important. As well as identifying code numbers from abbreviations of their descriptions, the search can display a description given a code number.