Only accept package names that are valid according to Debian Policy.

Improve title for the search page to mention experimental too.

Make title include the package name so package is more visible.

Make title mention if there are no excuses for the package.

Add link to the testing/experimental page from the opposite page.

Use same text on the forms as in the new links, expanded for clarity.

Refactor internals of suite selection.

Comment code that is immutable due to external assumptions.

Fixes: commit b87670b3