...

Here we define a set of rules that will all be executed in the file's order. The key string should evaluate as a python expression and return True once substituted.

There are a number of available substitution tokens:

...

"'_i8t' in '%(img_name)s'": {
	"args": {
		"texture_format": "tiff",
		"data_type": "byte"
	}
}

... matches "_i8t" in the image name, which is here interpreted as shorthand for "8 bits integer tiff format" and sets the texture format to "tiff" and the image to "byte" (8 bits integer, see txmake documentation). For example, a file named "roof_top_i8t_v01.png" would match that rule.

Of course, you can create more sophisticated tests by using the and and or keywords.

"'%(img_type)s' == 'float' and %(img_depth)d > 16"

The standard rules tend to rely on the node_type, img_type and img_depth to pick the best file format and compression algorithm.