The space before the a#39;Ua#39; clues TeX that the cs is complete. ... The definition of \ startit on line 86 tells TeX it needs to read material until it encounters a character whose ASCII value is 13 (the AAM on line 86) and catcode is 12 (line 85). So, TeXanbsp;...
|Title||:||TeX Reference Manual|
|Publisher||:||Springer Science & Business Media - 2012-12-06|