Is it safe to learn PHP 4?

[natethegreat!]

Someone loaned me a book on PHP 4, and as I don't know too much about it, except that it's a very old book (from 2000) and that their are newer versions of PHP, I'm wondering: Is it safe to learn PHP 4? Will it make it harder to use current PHP well and efficiently?
Thanks much,
NatetheGreat

[VHockey86]

all the basics are the same between php4 and php5. Its certainly not dangerous to learn it

[ShuckyD]

and to add to it PHP: Hypertext Preprocessor is a very good resource if your book doesnt cover functions and variable types as in depth as you would like. There are also good tidbits on there about the differences between 4 and 5

[natethegreat!]

Thanks so much for your help!