why dtd is not affecing my xml?

I am trying to run my own DTD to validate some XML codes, but it seems that the DTD doesn't affect the XML, here is my code:

<?xml version="1.0" standalone="yes"?>
<!DOCTYPE document [
<!ELEMENT document (title?)>
<!ELEMENT title (#PCDATA)>
<!ATTLIST title num ID #REQUIRED
info CDATA #IMPLIED>
]>
<document>
<title>the title</title>
</document>

so how I can solve this issue?