Why required attribute doesn't work in my form? I am using chrome dev 60.0.3074.0

<?php
$entryDataFound = isset($entryData);
if($entryDataFound === FALSE){
    $entryData = new stdClass();
    $entryData->entry_id= 0 ;
    $entryData->title = "";
    $entryData->entry_text = "";
    $entryData->message="";
}
return "      
<form method='post' action='admin.php?page=editor' id='editor' >
<input type = 'hidden' value = '$entryData->entry_id' name= 'id' />
            <fieldset>
                <legend> New editor form type the text in it.</legend>
                
                <label>Title</label>
                <input type='text' name='title' maxlength='150' value =' $entryData->title'  required >
                
                
                <label>Entry<label>
                <textarea name='entry' >$entryData->entry_text</textarea>
                
                <fieldset>
                            <input type='submit'  value='Save'  name='action'/>
                            <input type='submit'  value='Delete' name='action' />
                            <p id='editor-message'>$entryData->message</p>
                </fieldset>

            </fieldset>
</form>
";