\input question

With an tex file

---\input x.tex\relax---\bye

and a few input files x.tex either empty or containing a blank, or
percent sign, or letter a, or letter a and percent sign (and really only
these letters are in, checked with od), I get the following dvi output:

x.tex        dvi
---------------------
<> (empty)   ---
             ---
< >          ---
             ---
<%>          ------
<a>          ---a ---
<a%>         ---a---

I don't get the logics of this, also couldn't find an answer in the
TeXbook. Why is an empty file differently treated from a <%> file? And
why makes < > a par, but <a> makes an additional blank?

Regards, Hartmut