Debugger is one of core developer tools, that is provided by In-Portal. It shows all the things, that were done (e.g. database queries), while page was rendered after it's been sent to user. It also displays stack traces for exceptions and fatal errors in which value of each parameter in function call is displayed. This all sounds cool, but when value of parameter is huge array (e.g. > 300 entries), then seeing all of them in debugger won't be that helpful. For such huge arrays seeing a portion of array is usually enough to get an idea how other array content might look like.
For arrays, that have more than 50 keys show only first 50 keys and "...".