Are you sure, whether it is _new or _newtab?
There is no value called _newtab for target attribute.
May this SO answer gives us a better information,
Using target="_new" is technically invalid according to the
specifications, but as far as I know every browser will behave the
same way:
- it will search for a tab or window with the context name "_new" *
if a "_new" tab/window is found, then the URL is loaded into it * if
it's not found, a new tab/window is created with the context name
"_new", and the URL loaded into it
Note target="_new" will behave exactly the same as target="new",
and the latter is valid HTML while the former is invalid HTML.
These are possible values for target attribute: _blank, _self, _parent, or _top
I think what you're trying to refer is target-new, a CSS3 property.
The target-new property specifies whether new destination links should
open in a new window or in a new tab of an existing window.
target-new:window; //Opens a link in new window
target-new:tab; //Open a link in new tab
Note: The target-new property is not supported in any of the major browsers.