Action Region, Required Field and HTML5 Page

RequiredHTML5.page

<apex:page controller="RequiredCtrl" tabstyle="Account" doctype="html-5.0">
  <apex:pageMessages id="msgs"/>
  <apex:form>
    <apex:pageBlock mode="maindetail">
      <apex:pageBlockButtons location="top">
        <apex:commandButton value="Save" action="{!save}" />
      </apex:pageBlockButtons>
      <apex:pageBlockSection title="Account Information">
        <apex:pageBlockSectionItem>
          <apex:outputlabel value="Name"/>
          <apex:inputfield value="{!Acc.Name}"/>
        </apex:pageBlockSectionItem>
      </apex:pageBlockSection>
      <apex:outputPanel id="rows">
        <apex:actionRegion>
          <apex:pageBlockSection title="Related Information" columns="1">
            <apex:pageBlockSectionItem>
              <apex:commandButton value="Add Row" action="{!addRow}" rerender="rows,msgs"/>
            </apex:pageBlockSectionItem>
            <apex:pageBlockTable value="{!rows}" var="row">
              <apex:column headerValue="Value 1">
                <apex:inputText value="{!row.val1}" />
              </apex:column>
              <apex:column headerValue="Value 2">
                <apex:inputText value="{!row.val1}" />
              </apex:column>
              <apex:column headerValue="Value 3">
                <apex:inputText value="{!row.val3}" />
              </apex:column>
            </apex:pageBlockTable>
          </apex:pageBlockSection>
        </apex:actionRegion>
      </apex:outputPanel>
    </apex:pageBlock>
  </apex:form>
</apex:page>