如何创建自己的'Smarty'标签

what is the simplest method to do the following

Look at a block of text and anywhere it finds %sometxt% replace that with something else,

So basically any text that is enclosed within a set of percentage signs similar to how Smarty do this?

The simplest method you asked for:

$blockOfText = str_replace('%sometxt%', 'something else', $blockOfText);

You just replace it with str_replace.

$newText = preg_replace('/%.+?%/', 'replacedText', $text);

Should do it. replacedText needs to be whatever you want to replace %sometxt% with.

The regexp %.+?% means

Fine a % sign, followed by any character until I find another % sign.

The ? makes the expression 'lazy', so it will match up to the first occurrence of %.