For ‘Local HTML’ sessions, you can change the active session tab by using an HTML <A> tag. The following lists available URL paths for such purpose:

/.pkgdview?cmd=tab&next={relative-jump-count}
<a href="/.pkgdview?cmd=tab&next=1">Next session tab</a>
<a href="/.pkgdview?cmd=tab&next=3">Third next session tab</a>
<a href="/.pkgdview?cmd=tab&next=-1">Previous session tab</a>
<a href="/.pkgdview?cmd=tab&next=-2">Second previous session tab</a>
/.pkgdview?cmd=tab&idx={absolute-tab-index}
<a href="/.pkgdview?cmd=tab&idx=0">First session tab</a>
/.pkgdview?cmd=tab&open={session-name}
<a href="/.pkgdview?cmd=tab&open=Chloe">Open a session item named ‘Chloe'</a>