I use notepad++ and when I tried to add some PHP inside an HTML value property all the strings transformed into an URL. Even spaces inside the <?php ?>tags are replaced with URL underscores. Do you have any idea why this happens ? Is it a notepad++ bug or something?
Notepad++ is not transforming anything. Notepad++ is recognising some pieces of text as looking-like-a-url and it is changing the way those pieces are displayed. The mechanism is similar to how Notepad++ understands some other file types (such as programming languages) and it displays the different types of language item (comments, keywords, strings, etc) in different ways.