Parameter is only used for precondition checks

      The query parameter in HTML is a part of the URL that is used to pass information from a web page to the server. It is typically used for precondition checks to determine certain conditions before processing a request. 

      For example, let's say we have a web page that allows users to search for products. The URL of the page will be something like:
      http://example.com/search?query=product

      Here, the "query" parameter is used to pass the search term "product" to the server. The server can then perform a precondition check to validate the search term, sanitize it, and process the request accordingly.

      The query parameter can also have multiple values. For example:
      http://example.com/search?query=product&category=electronics

      In this case, the "query" parameter has the value "product" and the "category" parameter has the value "electronics". The server can use these values to perform more advanced precondition checks or filter the results based on the provided parameters.

      It's important to note that query parameters are not limited to search functionality only. They can be used for various purposes like sorting, filtering, pagination, etc. depending on the requirements of the web application.

      To retrieve the values of query parameters in HTML, you can use JavaScript or server-side programming languages like PHP, Python, etc. Here's an example using JavaScript:

      
         let urlParams = new URLSearchParams(window.location.search);
         let query = urlParams.get('query');
         console.log(query);
      

      This JavaScript code retrieves the value of the "query" parameter from the URL and logs it to the console.

      Overall, query parameters are essential for passing information from a web page to the server and are widely used for precondition checks and other functionality in web applications.