> In the menu, select User > Customize Completion. Then add \begin{flalign} to the list of commands. You can also specify arguments using @, e.g \foobar{@}. > from https://tex.stackexchange.com/a/185942 and > All the "@" characters in the code are automatically replaced by "•" place holders in the editor and the cursor will jump directly to the first "•" field (if some text has been selected in the editor before, the first "•" field will be replaced automatically by the selected text). Note : @@ will be replaced by the @ character in the editor (and not by a double placeholder) > from https://www.xm1math.net/texmaker/doc.html#SECTION33