Add Str::isHtml() method

[vaites]

Something like str($string)->isHtml() can be useful. This can be implemented in both Str (as an static method) and Stringable classes just using strip_tags to avoid new dependencies.

This method implementation was rejected twice before:

• Pull Request 516: in 2013 @taylorotwell did not want to integrate it
• Pull Request 37222: wrong implementation

But I'm asking again because methods like isJson() have been implemented. I can send a PR with tests if you want, but don't want it to be rejected if you do not agree...

[bert-w]

hm they seem like handy functions, although I happen to never have needed them.

The implementation of that first PR for isHtml seems too simple though:

public static function isHtml($string)
{
    return strlen(strip_tags($string)) < strlen($string);
}

i.e. "anything with a tag is html". I can imagine that there will be a lot of edge cases since strictly speaking you have to abide by the whole HTML spec in order to judge it is valid. <p><a>x</p></a> is not valid HTML for instance.

[vaites]

I didn't want to add an strict validation of HTML (<p><a>x</p></a> is not valid but is HTML), just check if a string contains any tag. Web browsers understands bad HTML, so this helper can do it too.

Using strip_tags seems to be the right approach for this, and in the future an extra argument for stricter validation can be added.