Test: The last test case in http://w3c-test.org/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/parsing.html
Specification: https://html.spec.whatwg.org/multipage/semantics.html#attr-meta-http-equiv-refresh

7. ... If the sequence of characters collected is the empty string, then no number will have been parsed; abort these steps. ...

IMO, these steps should be updated so that they accept numbers starting with "." because IE11, Edge, Firefox, and Google Chrome work so.