Hello, reffort@github (https://github.com/reffort) did notice a major issue in one of the key features of Heirloom roff which is paragraph-at-once formatting. Gunnar very likely did implement this algorithm based on the 1981 Knuth-Plass paper (KP-81 in the following text) and had maybe not been aware that TeX had implemended a slightly different algorithm later after gaining more experience in that field (TeX82 in the following text). But even KP-81 is implemented incorrectly to such a degree, that paragraph formatting in current Heirloom is noticeable far from being optimal. The full story of reffort's analysis and change proposal can be read at https://github.com/n-t-roff/heirloom-doctools/issues/22
There are two issues in Heirloom with that. One is the scaling of the deviation from the ideal interword space size (which allows too tight lines). A second issue is the use of that scaled value in the badness and demerits calculation. Here Gunnar maybe did misinterpret KP-81, the implementation is obviously wrong. reffort did not only provide a solution for these issues, he also provided a test document and the possibility to process this document with the algorithm described in KP-81, TeX82, two new proposals and current Heirloom (see https://github.com/n-t-roff/heirloom-doctools/issues/22). Heirloom users are encouraged to test these algorithms (also with their own documents) so a final decision regarding the changes could be made. --Carsten
