> 'd like to allow HTML code in my forum but I don't know how
Ahem, did you read the bit about security?
You'd be better off allowing certain BBCodes than giving somebody carte-blanche to paste in any old rubbish. Leaving off certain close tags could mess up your page layout or js scripts could hijack the page.
Thanks guys for all your care for the security of my forum but I'd sincerely like someone to tell me how to allow it. I also got the information that allowing HTML in phpBB3 is disabled because of security reasons but I'm still not sure if it's 100% true.
Although you could do it, it doesn't mean that you should. The HTML facility was taken out of phpBB3 AFAIK due to security issues. You seem absolutely determined to go through with it. Here's a phpBB3 mod that will allow you to enable HTML:
You need to ensure that you strip out any <script> or <link> stuff and that all tags are properly closed. For example if an user were to post '<strong>jvwjnvj' and leave it at that, would that then show the rest of the page below his displayed message as BOLD type? You are trusting users to create well-formed html and not to post malicious js or css.
> When you mention the entities(), do you think only to substitute these <> with these ()?
I am asking because I have already tried that and it didn't work.