\hsize=7cm
\parindent=0pt
\tracingoutput1
\showboxdepth\maxdimen
\showboxbreadth\maxdimen
\def\test#1{%
   \vbox to 0pt{\vrule height 1cm\hfill\vrule height 1cm \vss}
   \leavevmode\llap{#1 }\ignorespaces}

\test1
\pdfappendkern=1
\pdfprependkern=1
\pdfprotrudechars=2
\knbccode\font`\A=150
\knaccode\font`\A=150
\lpcode\font`\A=500
\rpcode\font`\A=500
text text text text text
text text text AtextA AtextA

\test2
\pdfprotrudechars=0
\knbccode\font`\-=250
\knaccode\font`\-=250
text text text text text text
text text text-text-text

\test3
text text text text text text
text text-text\-text-text

\bye