Ensure that the default initial value is given to the text box when the page is opened, and the text box content does not disappear after the submit-php Tutorial

Ensure that the default initial value is given to the text box when the page is opened, and the text box content does not disappear after the submit. ask your predecessors a question.
Now there is a text box. to prevent the content from disappearing after the submit is submitted, I write as follows:

However, I plan to give the text box a default value when opening the page (I have to initialize a value for the value). how can these two problems be compatible?

Reply to discussion (solution)

When submitting a webpage jump, you have to assign the value to the text box.
Ajax submission. you can leave the value of the text box empty.