Spaces When Concatenating Strings in PHP

Let two strings be stored in variables, and when concatenating them, we want to insert a space between them. This is done as follows:

php<?php
  $str1 = 'abc';
  $str2 = 'def';
  echo $str1 . ' ' . $str2; // outputs 'abc def'
?>

Let there be only one variable:

php<?php
  $str = 'abc';
  echo $str . ' ' . 'def'; // outputs 'abc def'
?>

In this case, there is no point in treating the space as a separate line - we'll insert it as part of the second term:

php<?php
  $str = 'abc';
  echo $str . ' def'; // outputs 'abc def'
?>