Block Sequences

A block sequence is a list with - markers per item.

fruits:
  - apple
  - banana
  - cherry

Each item starts with - followed by the item value.

Items can be:

• Scalars: strings, numbers.
• Maps: indented after -.
• Lists: nested.

Map items:

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

Each - starts a new map. The map's keys are at one indent more than the -.

Subtle: the name key's indent is BEYOND the - indent. The map under each - includes everything at that deeper indent.

Nested sequences:

matrix:
  - - 1
    - 2
    - 3
  - - 4
    - 5
    - 6

Yields [[1,2,3],[4,5,6]]. Each - opens a list within the parent list.

Mix of types in one list: allowed (heterogeneous).

mixed:
  - 1
  - hello
  - true
  - {key: value}

Empty list:

items: []

Or:

items:

Whether items: (no value) is empty list or null depends on parser; some treat as null.

Common operations:

• Iterating: for item in cfg['items'].
• Reading per-item maps: cfg['people'][0]['name'].

Style choice: which indent for -?

# Option A: marker at parent indent
items:
- one
- two

# Option B: indent more
items:
  - one
  - two

Both valid YAML 1.2. Option B is more common in modern style guides.