Having solved my last problem, for my next trick, I have created a reasonably complicated flowchart with some in-page connectors. These, I hypelinked.
I found out by plodding through various sites that I can change the default zoom level so that the links open up in the right zoom level – if you don’t, clicking the link on the shape takes you to the default level of “whole page” which is not particularly helpful. I set these to have 150% zoom, which means that the shape is readily visible and you can see where to go. In the shape, you set the hyperlink as:
Address: ?zoom=150
Sub-address: Page-1Object.123
Text: Link to connector 1
(although note that you can also set the zoom by clicking on Browse on Sub-Address – but it gets put in the Address section anyway so you might just as well type it there)
This works exactly as intended in Visio. But when I export to VML, oh dear. First of all, I have to manually correct the VML shape file as described by Hans in my earlier post 657383. But a) the text description has not been added – it’s just the text on the connector – and 
the zoom doesn’t work AT ALL – it only goes to whole page and nothing else. I can manually edit the VML_1.HTM to find the text (for reference, it is the origTitle= section in the shape definition) but I cannot find, anywhere, any information about setting the zoom level.
Been everywhere I can think of online to see if anyone else has the problem, but nothing.
Help? 
