I know how to add custom meta tag in a Magento 1 CMS page using 'Layout Update XML' option.
<reference name="head">
<block type="core/text" name="custommeta">
<action method="setText">
<text>
<![CDATA[<meta data-customid="customid_meta_1" />]]>
</text>
</action>
</block>
</reference>
How I can add meta tag in the same way for a specific CMS page in Magento 2 using option 'Layout Update XML'
<meta data-customid="customid_meta_1" />