ms html clipboard format CF_HTML handles table like below if we copy part of table.
it makes problem when copying table from ms product such as ie, excel, powerpoint then pasting to squire.
<TABLE BORDER>
<!--StartFragment-->
<TR><TD>Item 6</TD><TD>Item 7</TD></TR><TR><TD>Item 10</TD><TD>Item 11</TD></TR>
<!--EndFragment-->
</TABLE>
and
<TABLE BORDER><TR>
<!--StartFragment-->
<TD>Item</TD>
<!--EndFragment-->
</TR></TABLE>
https://msdn.microsoft.com/en-us/library/windows/desktop/ms649015(v=vs.85).aspx#274
This allows any level of indentation for bullets. It does this by introducing
invalid HTML. In particular, you can make bullets like:
<ul>
<ul>
<li>foo</li>
</ul>
</ul>
1. Keeps all leaf nodes not just text nodes, so images etc. are not removed.
2. If the selection is not within a single block, it is expanded to the edges
of the blocks rather than splitting the blocks; this is unlikely to have
been what the user wanted.
3. More efficient tree traversal and manipulation; no duplication of nodes.
4. Records undo state before performing the action.
