From the XHTML 1.0 Spec
In XML, fragment identifiers are of type ID, and there can only be a single attribute of type ID per element. Therefore, in XHTML 1.0 the id attribute is defined to be of type ID. In order to ensure that XHTML 1.0 documents are well-structured XML documents, XHTML 1.0 documents MUST use the id attribute when defining fragment identifiers on the elements listed above. See the HTML Compatibility Guidelines for information on ensuring such anchors are backward compatible when serving XHTML documents as media type text/html.
For multiples, it needs to be classes. You can have two classes like this
<div class="Airport Pick-up">
and that would be styled in the CSS like this
And even that might not be valid since they start with caps.