there is a default chapter that can be used to give default key/values for all the other chapters
the default chapter name is [default] but this can be changed to e.g. [_default] or [def-values]

[default]
key1=1

[chapter1]
// key1 will exist and = 1
key2=2

{parameter} substitution

key names can be used as variables in value definition and will be substituted when the value is consulted.
The variable syntax is {key} by default, but can be changed to e.g. {$key} or [key]

[default]
domain=www.example.com

[chapter1]
code=4567
url=https://{domain}}/?code={code}
// url will be = https://www.example.com/?code=4567