Indentation Rules

YAML uses indentation for structure. Critical rules:

1. Spaces only, NO tabs (mixing breaks parsers).
2. Indentation level = number of leading spaces.
3. Children indented MORE than parent.
4. Siblings at SAME indent level.

parent:
  child1: value
  child2:
    nested: value
  child3: value

Indent count is consistent within a block but flexible between blocks. Best practice: 2 spaces per level.

Common errors:

# BAD: tabs
parent:
	child: value

# BAD: inconsistent
parent:
  child1: value
   child2: value     # 1 extra space

# OK
parent:
  child1: value
  child2: value

Lists (sequences):

items:
  - apple
  - banana
  - cherry

The - is a list marker; indentation tracks the parent.

Block list inside map:

fruits:
  - apple
  - banana

veggies:
  - carrot

Two equivalent indentations:

items:
- apple        # marker at parent's level (allowed)
- banana

items:
  - apple      # marker indented MORE (also allowed)
  - banana

Both valid. Style varies; explicit indent is clearer.

Map of lists:

colors:
  primary:
    - red
    - blue
    - yellow
  secondary:
    - green
    - orange
    - purple

Mixed nesting:

people:
  - name: Alice
    age: 30
  - name: Bob
    age: 25

The - starts a list item that's a map.

Linters help (yamllint).