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+[[!meta title="Typesetting scenario steps based on matched bindings"]]
+[[!tag pondering]]
+[[!meta date="2019-11-30 09:34"]]
+
+We're working on typesetting scenarios. The first iteration of this
+aims at the following:
+
+* Subplot reads the markdown input, and a YAML file with bindings. The
+  YAML file is named in the markdown's metadata block (a Pandoc
+  extension to markdown).
+* The bindings may capture parts of a step using regular expressions.
+* Each scenario snippet is typeset separately.
+* Each step in a snippet is typeset separately.
+* There is no support for "and" or "but". The keyword must be one of
+  "given", "when", or "then".
+* The keyword of a step is typeset in italics.
+* Captured parts of a step are typeset in bold face.
+* The rest of the step is typeset in a normal font.
+* Steps that do not match a binding, or have an unknown keyword, or
+  otherwise are problematic, are typeset in monospace and have a
+  question mark prepended to them. A descriptive error message is
+  added to the document as well.
+
+To implement this, I'm going to want a couple of abstractions:
+
+* A snippet parser, as an iterator over unparsed steps (string
+  slices).
+* A step parser, which takes an unparsed step (a string slice), and
+  returns a parsed step.
+
+A parsed step is matched against all known bindings. It can either be
+a successful match, or an unsuccessful one.
+
+A successful match consists of a step kind (keyword), and a list of
+partial steps. A partial step is either captured or uncaptured parts
+of the step.
+
+Given a binding file like this:
+
+```yaml
+- given: I am (?P<name>\S+)
+- when: I declare myself (king|queen)
+- then: everyone agrees
+```
+
+And a scenario snippet like this:
+
+```
+given I am Tomjon
+when I declare myself king
+then there is applause
+```
+
+This would result in the following parse results:
+
+* A matched step, with keyword _given_, an uncaptured part "I am " and
+  a captured part "Tomjon"
+* A matched step, with keyword _when_, and an uncaptured part "I
+  declare myself king"
+* An unmatched step, with text "then there is applause"
+