Glossary

Alias — a reference to an anchored value, written *name. Wherever an alias appears, the anchored value is what the parser delivers.

Anchor — a name attached to a value where it's defined, written &name, so the value can be reused by alias or merged elsewhere.

Block style — the indented layout: mappings as key: value lines, sequences as - lines. The opposite of flow style.

Chomping — what happens to a block scalar's final newline: clip (keep one, the default), strip (keep none, -), or keep (keep all trailing blank lines too, +).

Document — one complete value in a YAML stream. Files usually hold one; several are separated by --- lines and loaded with an _all-style loader.

Dump — turning data structures back into YAML text (yaml.safe_dump in Python). Keys come out sorted, comments don't survive, and strings that would re-read as another type are quoted for protection.

Explicit tag — a type written into the file: !!str 8080. Overrides the parser's implicit guess; rarely needed beyond forcing.

Flow style — the bracketed one-line layout, [8080, 8443] and {name: beacon}, borrowed from JSON. Any collection can be written either way.

Folded scalar — a block scalar introduced by >: single line breaks become spaces, for prose. Its sibling, the literal scalar (|), keeps line breaks exactly.

Implicit typing — the parser's rules for guessing a scalar's type from its shape: digits become numbers, certain words booleans, date-shaped text (in some parsers) dates. Chapter 8 is what happens when it guesses wrong.

Key — the left side of a mapping entry. Keys are values too and get implicit typing of their own — which is how on: becomes the key True under YAML 1.1 rules.

Mapping — key/value pairs; what Python calls a dict and JSON calls an object. Written key: value, one per line.

Merge key — <<, whose value is an alias (or list of aliases) to a mapping whose keys are poured into the current one. Keys written out locally win.

Node — any single piece of a YAML document: a scalar, a sequence, or a mapping. The word parsers and the specification use.

Null — YAML's "no value", spelled null, ~, or nothing after the colon. Not the same as the empty string ''.

Plain scalar — an unquoted value: beacon, 8080, 1:20. Cheapest to write, and the only style the parser freely reinterprets.

Safe loader — a loader that constructs only plain data (strings, numbers, booleans, lists, mappings, standard types) and refuses tags that name program objects. The only loader to use on files you didn't write.

Scalar — a single value: string, number, boolean, or null.

Sequence — an ordered list, written with - lines in block style or [ ] in flow.

Sexagesimal — base-60 notation, 1:20 meaning 80 under YAML 1.1 number rules. Removed in YAML 1.2; one of the famous traps until then.

Stream — a whole YAML input: one or more documents, possibly with --- separators and ... end markers.

YAML 1.1 / 1.2 — the two specification versions in circulation. They agree on structure and disagree on some scalar spellings — which words are booleans, whether 1:20 is a number, whether a timestamp becomes a date object. "Know your parser" is the short version.