php echo does not reflect on screen till end of processing

With the code at https://github.com/hn-88/mktxt/ found that sometimes the messages would not be displayed on screen till the end of execution.

https://stackoverflow.com/questions/4669822/echo-messages-while-php-script-still-executes

- so it may be client dependent.

And yes - found that in Edge / Chrome / Chromium, the output is shown as soon as the page opens, with dynamic updating. With my version of Firefox, the output flush does not work due to browser caching.