Weird behavior of urls() in string concatenation

[CalleRosa40]

Hi,

Why does this

<?php
$test = urls('templates');
$templateCSS = '
	<link rel="stylesheet" href="' . urls('templates') . 'styles/uikit.min.css">
	<link rel="stylesheet" href="' . urls('templates') . 'styles/tom-select.css">
';

work in PW 3.0.165 and not this?

<?php
$templateCSS = '
	<link rel="stylesheet" href="' . urls('templates') . 'styles/uikit.min.css">
	<link rel="stylesheet" href="' . urls('templates') . 'styles/tom-select.css">
';

Second snippet makes PW throw "Fatal Error: Uncaught Error: Call to undefined function urls() in ...". First snippet outputs okay. These are the first few lines of one of my templates.

Sorry, if this is a dumb question, but I really don't get it. Am I being blind? Can anyone put me on the right track? Thanks a lot.