Hello, When a line ends with a sequence whose direction differs from that of the paragraph, we risk pushing some text into the margin (when not necessary). Here is an example with corresponding output: \usemodule[simplefonts] \setmainfont[ALM Fixed][features=arabic,range=arabic] \setupalign[r2l] \setupwhitespace[big] \showframe \starttext % 10 copies of Persian word "hello" stay on one line. \dorecurse{10}{سلام } % 20 copies makes a 2-line paragraph. \dorecurse{20}{سلام } % one copy of the word goes into the margin although the Latin letters perfectly fit the line. \dorecurse{10}{سلام } {\textdir TLT\dorecurse{20}{a}} \dorecurse{10}{سلام } % although the Latin string extends into the margin, TeX still puts one copy of "hello" there as well. \dorecurse{10}{سلام } {\textdir TLT\dorecurse{30}{a}} \dorecurse{10}{سلام } % something similar happens here with the opposite par/text dir \pardir TLT \dorecurse{10}{bidi } {\textdir TRT\dorecurse{20}{آ}} \dorecurse{10}{bidi } \stoptext The problem seems to be that after typesetting the LTR text within the RTL paragraph, TeX thinks the current text ends at the left end of the LTR portion; hence, it tries to add something to the line; it's only after that that it discovers we ran into the margin! —MHB