BEGIN and END tags in PHPRUNNER output files

  html, php, phprunner

In the directory of a project made in PHPRUNNER, what expressions like {BEGIN grid block}, {END grid block}, {$ menu main}, etc. that appear in .htm files mean?

My interpretation is that these blocks of text are translated by the .php files when the program is building (if I inspect elements on the output page these blocks do not appear, they are replaced by additional codes), but I do not know how this supposed translation of these blocks for code is done.

Code example with these blocks

Source: Ask PHP