textbox.jelly (when autoCompleteUrl defined) and combobox.jelly both present a text field with special behavior: you can select likely completions from your browser.

Unfortunately there is no visual indication that these are anything other than plain text fields, and if you were not familiar with Jenkins and paying attention you might think that the completion popup was merely your browser’s form completion function, with no Jenkins domain information, which you would then be inclined to ignore.

Also completion appears to be case-sensitive, unlike typical completion UIs, reducing the likelihood that you would even see the completion popup at all. Ought to accept case-insensitive prefixes (correcting to the true case if the completion is accepted).