RE: line adjustment at the end of a sentence

[Drew Adams]

> The number of spaces between English sentences has been 
> gradually switching from two to one.

Dunno about that.  Mostly I think people just use plain text less and formatted
text more nowadays.

FWIW, English (at least the American variety) has typically used two spaces for
typewritten text, but some other languages (e.g., French) have used only one.
Other punctuation (e.g. `:', `;') also offers differences wrt spacing among
different languages.

> I've always been impressed by the way it handles "Dr. Watson" and
> similar uses of a single space that is not the end of a sentence.

Wrt filling, with non-nil `sentence-end-double-space', Emacs tends to treat a
single space after period somewhat like a no-break space.

There are also other sentence and spacing related user options in Emacs:
`colon-double-space', `sentence-end', `sentence-end-base',
`sentence-end-without-space', `sentence-end-without-period'.

> the ease with which one can act on sentences in Emacs.

Yup.