[libvirt] [PATCH] docs: Clarify usage of vram and heads

[Osier Yang]

Though attributes "vram" and "heads" of "video" element are generic,
they are only useful for vbox driver currently.

* docs/formatdomain.html.in
---
 docs/formatdomain.html.in |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 43c78fc..c130460 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -1572,6 +1572,8 @@ qemu-kvm -net nic,model=? /dev/null
	"xen" or "vbox", depending on the hypervisor features available.
         You can also provide the amount of video memory in kilobytes using
         <code>vram</code> and the number of screen with <code>heads</code>.
+        NB, though <code>vram</code> and <code>heads</code> are generic
+        attributes, they are only useful for vbox driver.
       </dd>

       <dt><code>acceleration</code></dt>
--
1.7.3.2