How do you use YAML indentation to control the scope and visibility of variables and parameters?

1 What is YAML indentation?

YAML indentation is the use of spaces or tabs to align the elements of a YAML document. Indentation creates a parent-child relationship between keys and values, and between collections and their items. The level of indentation determines the scope and visibility of variables and parameters, which are references to values that can be reused or overridden in different contexts. Indentation is essential for readability and maintainability of YAML files.

2 How to indent YAML files?

The recommended way to indent YAML files is to use two spaces per level of indentation, as tabs can cause parsing errors. You can use a YAML linter or formatter to check and correct your indentation automatically. Generally, when indenting YAML files, each line should start at the same level as the previous one unless creating a new level of hierarchy. Use a colon (:) to separate a key from its value, and a dash (-) to indicate an item in a sequence. Furthermore, brackets ([ ]) or braces ({ }) can be used to enclose a sequence or mapping in a single line with items separated by commas. Additionally, you may use a question mark (?) to indicate a complex key and an exclamation mark (!) for a tag. Lastly, use a pipe (|) or greater than sign (>) for block scalar, which is for writing multiline strings with one more level of indentation.

3 How to scope and override variables and parameters?

Variables and parameters are placeholders for values that can be defined, referenced, and modified in different parts of a YAML file. They can be useful for avoiding repetition, simplifying updates, and customizing outputs. To declare and use variables and parameters in YAML, use an ampersand (&) to assign an anchor (a name) to a value, and an asterisk (*) to reference it later. Additionally, double curly braces ({{ }}) are used to interpolate (insert) a parameter in a value, with a colon (:) assigning a default value to the parameter if it is not provided. To merge two mappings into one, use double angle brackets (<<), and specify the merge strategy (overwrite or append) with an exclamation mark (!). The scope and visibility of variables and parameters depend on where they are defined and used; generally, variables and parameters are visible within the same level of indentation or below, unless they are overridden by another declaration with the same name. To define a global variable or parameter, declare it at the top level of the file; to define a local variable or parameter, declare it within a specific key or value at the same level of indentation or below; to override a global variable or parameter, declare it with the same name at a lower level of indentation or use the overwrite merge strategy (!overwrite); and to append to a global variable or parameter, use the append merge strategy (!append).

5 How to learn more about YAML indentation?

YAML indentation is a powerful and flexible feature that allows you to create complex and dynamic data structures and configurations. However, it also requires attention and care to avoid mistakes and bugs. If you want to learn more about YAML indentation, you can check out the official YAML specification, the YAML tutorial, and some online YAML validators and converters. You can also practice your YAML skills with some online exercises and challenges.