Rules

Understand how Wenmode composes Markdown syntax from opt-in parser rules.

---

Rules are opt-in and composable. A parser only recognizes syntax for rules that you enable.

Read this page when you are building a custom dialect. If you only need common Markdown, start with Presets; if you need non-standard syntax packaged with renderer behavior, start with Plugins.

from wenmode import Wenmode
from wenmode.rules import AtxHeading, Emphasis, InlineCode

wen = Wenmode([AtxHeading, InlineCode, Emphasis])

With this rule list, ATX headings, inline code, and emphasis are parsed. Other Markdown syntax remains plain text unless another enabled rule handles it.

Empty and custom rule sets

Pass an empty list when you want no Markdown rules enabled.

from wenmode import Wenmode

wen = Wenmode([])
text = '# not a heading'

html = wen.render(text)

Pass classes or configured rule instances. Classes are instantiated automatically, while instances let you choose rule options.

from wenmode import Wenmode
from wenmode.rules import Image, Link

wen = Wenmode([
    Image(references=False),
    Link(references=False),
])

In this example, direct links and images are enabled, but reference-style links, reference-style images, and reference definitions are not.

Runtime registration

Rules can be registered after construction.

from wenmode import Wenmode
from wenmode.rules import AtxHeading

wen = Wenmode([])
wen.register_rule(AtxHeading)

register_rules() accepts multiple rules:

from wenmode import Wenmode
from wenmode.rules import AtxHeading, Emphasis, InlineCode

wen = Wenmode([])
wen.register_rules([AtxHeading, InlineCode, Emphasis])

Rules are stored by name. Registering another rule with the same name replaces the previous one.

Rule categories

Wenmode has three parser rule categories:

• BlockRule parses block-level syntax such as headings, lists, tables, and fenced code.

• ContinueRule can turn an already-started paragraph into another node, such as a setext heading or definition list.

• InlineRule parses inline syntax such as links, inline code, directives, and formatting.

Some rules also attach transforms. Node transforms mutate a node in place as soon as its owning block or continuation rule returns it. Root transforms collect document-wide definitions, defer inline resolution until the whole document is known, or update parsed nodes after block parsing is complete.

If a feature needs both syntax and output behavior, register it through a plugin so the rule and renderer handlers stay together.

Rule order

Block and inline rules are sorted by their order value. When multiple inline rules match at the same position, the sorted rule order decides which rule wins.

Most custom rules can keep the default order. Set a custom order only when your rule must run before or after another syntax with overlapping markers.

Prefer changing rule order in the smallest possible rule set and cover the overlap with tests. Rule order changes can affect unrelated syntax that shares the same opening character.

Inspecting enabled rules

The parser exposes enabled rules as a dictionary.

from wenmode import Parser
from wenmode.presets import commonmark

parser = Parser(commonmark)

if 'emphasis' in parser.rules:
    print('emphasis is enabled')

This is useful for rules that need to check whether another feature is enabled without assuming a fixed preset.

For the syntax, generated node type, AST shape, and default HTML output of each public rule, see Reference.