lex-primer

name: lex-primer description: | Primer for writing correct Lex documents. Use when: (1) Writing or generating .lex content (2) Understanding Lex syntax (it is NOT Markdown) (3) Reviewing whether a .lex file is syntactically correct (4) Converting content to Lex format

Lex Document Primer

Lex is NOT Markdown. It uses indentation and conventions from publishing — no # headers, no --- separators, no **bold**. If you write Markdown syntax in a .lex file, it will be treated as plain text.

Core Principle

Structure = indentation (4 spaces per level). The only explicit syntax marker is :: (for annotations/verbatim blocks). Everything else is determined by position, indentation, and punctuation patterns.

The Six Elements

1. Paragraph (fallback)

Consecutive non-blank lines. If nothing else matches, it's a paragraph.

This is a paragraph.
It can span multiple lines.

2. Session (heading + content)

A title line, then a blank line, then indented content.

1. Introduction

    This paragraph is inside the "Introduction" session.

    1.1. Background

        Nested session with its own content.

• Title can have an ordered marker (1., a., I.) or be plain text
• The blank line after the title is MANDATORY (distinguishes from definition)
• Content MUST be indented relative to the title

3. Definition (term + immediate content)

A subject line ending with :, then immediately indented content (NO blank line).

HTTP Methods:
    GET retrieves resources.
    POST creates new resources.

• NO blank line between subject and content (that would make it a session)
• Content can include paragraphs, lists, and nested definitions
• Cannot contain sessions

4. List (2+ items after blank line)

Two or more list-item lines preceded by a blank line.

Some intro text.

- First item
- Second item
- Third item

• Markers: - (dash), 1. or 1) (numbered), a. or a) (alpha), I. (roman)
• MUST have at least 2 items (single item = paragraph)
• MUST be preceded by a blank line (or document start)
• NO blank lines between items (blank line terminates the list)
• Marker style of first item defines the list style; mixing markers is allowed

5. Verbatim Block (raw content)

A subject line ending with :, optional blank line, indented raw content, and a closing :: annotation.

Example code:

    fn main() {
        println!("Hello");
    }

:: rust ::

• Content is NOT parsed (preserves raw text exactly)
• Closing :: label :: annotation is mandatory
• Marker form (no content): just subject + closing annotation

6. Annotation (metadata)

Structured metadata using :: markers.

:: note ::
:: warning status=open :: This needs review
:: aside ::
    Block content here.
    - Can include lists
::

Three forms:

• Marker: :: label :: (no content)
• Single-line: :: label :: inline text
• Block: :: label :: + newline + indented content + bare :: closing

Inline Formatting

*bold text*           — strong (NOT **double asterisk**)
_italic text_         — emphasis (NOT *single asterisk*)
`code`                — inline code
#math expression#     — math notation
[reference]           — reference/link

Reference types (determined by content):

• [https://example.com] — URL
• [@doe2024] — citation
• [^note1] — footnote (labeled)
• [42] — footnote (numbered)
• [#2.1] — session reference
• [./path/to/file] — file reference
• [TK] — placeholder (to come)

Escape with backslash: \*not bold\*, \[not a link\]

Common Mistakes (Lex ≠ Markdown)

Indentation Rules

• 1 level = 4 spaces (tabs converted to 4 spaces)
• Partial indentation (e.g., 6 spaces = 1 indent + 2 literal spaces) is tolerated
• Content must be indented deeper than its parent element
• Dedent returns to parent scope

Parse Precedence

The parser tries elements in this order:

1. Verbatim block (has closing annotation)
2. Annotation (:: markers)
3. List (blank line + 2+ items)
4. Definition (subject + immediate indent)
5. Session (title + blank line + indent)
6. Paragraph (everything else)