C-e i starts reading at point and continues towards the accessible end of the buffer. Unlike a line or paragraph inspection, it advances point as sentence-oriented chunks complete. This requires a speech server supporting tracked playback completion. An unsupported server reports that limitation; it does not silently provide equivalent position tracking.
Try it in an ordinary prose buffer, with no selection you need to preserve:
Stopping retains the beginning of the current chunk, not necessarily the last word you heard. Another user command interrupts tracked reading before performing its own action. A movement command therefore also changes the retained position, and ordinary typing can insert text there. Use the explicit Stop command when you want to listen, stop, and decide what to do next. An existing active region would change as point advances, so use C-e r, not C-e i, to check a selection.
Chunks prefer sentence boundaries and are bounded by
emacsvox-tracked-reading-max-chars, currently 280 source characters. This is
not a word count or an exact acoustic position. Completion reaches the saved
end of the accessible text; failure or interruption ends the reading session.
You can inspect the text and issue a new reading command without restarting
Emacs. On a backend without tracked support, read paragraphs or short regions,
or use the untracked buffer form with the size/layout limitations above.
For movement to another starting point, see Moving point in the GNU Emacs Manual. The speech commands themselves belong to Emacsvox; their exact interfaces are in the core speech reference.