Hi, a microtype user stumbled upon some bugs with \pdfappendkern/\pdfprependkern: (1) interaction with protrusion: if a glyph has a pre- or appended kern, protrusion will not work for this glyph, as pdftex will stop scanning at the inserted kern. This is certainly wrong, as this extra kern should not be considered as explicit but as implicit (but see below). It could easily be fixed, I think, by adding the auto_kern subtype to cp_skipable: pdftex.web, l. 24375: @d cp_skipable(#) == {skipable nodes at the margins during character protrusion} ( not is_char_node(#) and ( ... or ((type(#) = kern_node) and ((width(#) = 0) or (subtype(#) = normal) or (subtype(#) = auto_kern))) ... ) ) A further question would be whether the extra kern should be skipped only, or also discarded. This, I suppose, depends on how you see the prepend/append mechanism conceptually: should it be considered as adding kerning pairs with all other glyphs in the font, or as modifying the side bearings of the glyph in question. In the first case, the kern should be discarded (and in the example below, the "A" would be protruded by 500/1000em), in the second not ("A" protruded by (500-150)/1000em). For me it would be fine either way, as microtype could then adjust it anyway... (2) interaction with discretionaries: if an explicit hyphen (or two or three) has an appended kern, the discretionary following the hyphen will be inserted /before/ the kern, so that pdftex may break the line at this point, disjoining the appended kern from the glyph and carrying it over to the beginning of the next line. (3) interaction with hyphenation: in case of hyphenation, the discretionary hyphen does not receive any pre/appended kerns at all. (This one's actually older, but I either forgot to report, or it got lost, or rejected. In that case, I apologise.) Here's an example for all three issues: \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 Best, -- Robert