Alist chains (Extending LilyPond)

#### Alist chains

An alist chain is a list containing property alists.

The set of all properties that will apply to a grob is typically stored as an alist chain. In order to find the value for a particular property that a grob should have, each alist in the chain is searched in order, looking for an entry containing the property key. The first alist entry found is returned, and the value is the property value.

The Scheme procedure `chain-assoc-get` is normally used to get grob property values.

#### Extending LilyPond v2.26.0 (stable-branch).

- 1 Scheme tutorial
  - 1.1 Introduction to Scheme
    - 1.1.1 Scheme sandbox
    - 1.1.2 Scheme variables
    - 1.1.3 Scheme simple data types
    - 1.1.4 Scheme compound data types
      - Pairs
      - Lists
      - Association lists (alists)
      - Hash tables
    - 1.1.5 Calculations in Scheme
    - 1.1.6 Scheme procedures
      - Defining procedures
      - Predicates
      - Return values
    - 1.1.7 Scheme conditionals
      - if
      - cond
  - 1.2 Scheme in LilyPond
    - 1.2.1 LilyPond Scheme syntax
    - 1.2.2 LilyPond variables
    - 1.2.3 Debugging Scheme code
    - 1.2.4 Input variables and Scheme
    - 1.2.5 Importing Scheme in LilyPond
    - 1.2.6 Object properties
    - 1.2.7 LilyPond compound variables
      - Offsets
      - Fractions
      - Extents
      - Property alists
      - Alist chains
    - 1.2.8 LilyPond’s box model
    - 1.2.9 Internal music representation
  - 1.3 Building complicated functions
    - 1.3.1 A first approach (example)
    - 1.3.2 Displaying music expressions
    - 1.3.3 Music properties
    - 1.3.4 Doubling a note with slurs (example)
    - 1.3.5 Adding articulation to notes (example)
- 2 Interfaces for programmers
  - 2.1 LilyPond code blocks
  - 2.2 Scheme functions
    - 2.2.1 Scheme function definitions
    - 2.2.2 Scheme function usage
    - 2.2.3 Void Scheme functions
  - 2.3 Music functions
    - 2.3.1 Music function definitions
    - 2.3.2 Music function usage
    - 2.3.3 Simple substitution functions
    - 2.3.4 Intermediate substitution functions
    - 2.3.5 Mathematics in functions
    - 2.3.6 Functions without arguments
    - 2.3.7 Void music functions
  - 2.4 Event functions
  - 2.5 Markup functions
    - 2.5.1 Markup construction in Scheme
    - 2.5.2 How markups work internally
    - 2.5.3 New markup command definition
      - Markup command definition syntax
      - On properties
      - A complete example
      - Adapting builtin commands
      - Converting markups to strings
    - 2.5.4 New markup list command definition
  - 2.6 Contexts for programmers
    - 2.6.1 Context evaluation
    - 2.6.2 Running a function on all layout objects
  - 2.7 Callback functions
  - 2.8 Unpure-pure containers
  - 2.9 Difficult tweaks
- 3 LilyPond Scheme interfaces
- Appendix A GNU Free Documentation License
- Appendix B Index