When you press the search button on the search special page several times, then search URL parameters disappear in the address bar of the browser.
- open Special:Search
- by wikilink https://en.wikipedia.org/wiki/Special:Search or through the search box at the top corner
- you will see https://en.wikipedia.org/wiki/Special:Search?ns0=1 or https://en.wikipedia.org/w/index.php?search=&title=Special%3ASearch&go=Go&ns0=1
- click the blue search button
- click the blue search button again
- you will see url https://en.wikipedia.org/w/index.php
You can enter different text for search on each of these three steps. But it ends with the fact that you can not copy the URL for pasting it somewhere or save it, because ULR becomes "index.php" without parameters.