How to manage custom error message with php - php

Question

How can I put a custom error message with php? The x-moz-errormessage works great but not so the oninvalid="this.setCustomValidity.
// Formular erstellen
$Formular = $javascript . '
<br><p class="button_center"><a class="btn btn-primary" href="feedback_en.php">to the feedbacks</a></p>
<form name="Form" action="feedback_en.php?eintragen" method="post" accept-charset="UTF-8">
<p><br>
<label class="form-control-label">Your name
<input required="" oninvalid="this.setCustomValidity('Please fill this field.');" onchange="try{setCustomValidity('')}catch(e){};" x-moz-errormessage="Please fill the field!" type="text" class="form-control" name="name" value="' . $name . '" size="35" maxlength="35">
</label>
</p>
'

Answer 1

Escape the surrounding apostrophs in setCustomValidity('Please fill this field.'), so that they can be treated by PHP as literal characters, not as closing/opening characters of a PHP string.
Read Escape sequences.
So, correct is:
$Formular = $javascript . '... oninvalid="this.setCustomValidity(\'Please fill this field.\');" ...';
If, for example, you are writing this simple PHP code in an test.php page:
<?php
$myName = 'My name is 'Julie'.';
echo $myName;
then you'll receive the following error:
Parse error: syntax error, unexpected 'Julie' (T_STRING) in
[path-to]/test.php on line 3
Whereas the following code with escaped apostrophes will work:
<?php
$myName = 'My name is \'Julie\'.';
echo $myName;