Do I need a trailing semicolon here?

Example:

<?php $formElement->display()?>

Is this fine, or should I provide a ; ? Well I guess that the PHP interpreter is clever enough to see that the line is finished and the expression done because of the ?> at the end开发者_StackOverflow社区. Right?

It is not required, but you should put it, as a good practice.

That way, the day you need to add another instruction after this one, it'll work fine.

And here is the manual's page that answers your question : Instruction separation (quoting, emphasis mine) :

As in C or Perl, PHP requires instructions to be terminated with a semicolon at the end of each statement.
The closing tag of a block of PHP code automatically implies a semicolon; you do not need to have a semicolon terminating the last line of a PHP block.
The closing tag for the block will include the immediately trailing newline if one is present.

No, the closing ?> will automatically close the line.

From the PHP Docs:

The closing tag of a block of PHP code automatically implies a semicolon; you do not need to have a semicolon terminating the last line of a PHP block.

As you say, the PHP interpreter will cope as-is.

However, I'd say that adding the semicolon is probably slightly better practice, but that's just a personal coding preference.

Simple answer: yes. It's okay to only have one statement without a semicolon inside PHP tags.