Diff Highlighting

Diff highlighting combines unified diff markers with full syntax highlighting. Lines starting with + and - are marked as insertions and deletions while the code is highlighted in the original language rather than plain diff syntax.

Hybrid diff syntax

Set the language to diff and specify the original language with lang=:

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```diff lang="go" title="hybrid-diff.go" showLineNumbers
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 import (
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-    "fmt"
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+    "log"
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     "os"
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 )
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 func main() {
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-    fmt.Println("hello")
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+    log.Println("hello")
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 }
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```

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import (
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   "fmt"
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   "log"
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    "os"
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)
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func main() {
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   fmt.Println("hello")
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   log.Println("hello")
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}

→ Lines prefixed with + show green insertion markers. Lines prefixed with - show red deletion markers. Context lines and the code are highlighted with Go syntax colors.

Any language supported by the configured highlighter can be used with lang=:

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```diff lang="javascript" title="config.js"
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 const config = {
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-  port: 3000,
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+  port: 8080,
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   host: "localhost",
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 };
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```

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const config = {
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 port: 3000,
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 port: 8080,
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  host: "localhost",
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};

→ Port 3000 shows a red deletion marker. Port 8080 shows a green insertion marker. The block uses JavaScript syntax highlighting.

How it works

Two conditions activate hybrid mode: the language must be diff AND lang= must specify the original language. The preprocessor runs before syntax highlighting:

1. Strips the +, -, or leading space prefix from each line
2. Generates ins line markers for + lines and del markers for - lines
3. Passes the stripped code to the highlighter using the lang= language

Lines with no recognized prefix (not starting with +, -, or space) pass through unchanged. Empty lines are kept as-is. If the prefix is "+ " (with a space), both characters are stripped. If it is "+foo" (no space), only the + is stripped.

After processing, the block effectively becomes the underlying language. The toolbar badge, data-language attribute, and language detection all reflect the swapped language.

The +/- indicators in the rendered output are CSS ::before pseudo-elements on .kz-code, driven by the --kz-ins-indicator and --kz-del-indicator variables. No diff-specific CSS or JavaScript exists. Diff highlighting reuses the line marker infrastructure entirely.

Plain diff mode

Without lang=, a diff block renders as plain diff syntax with no Kazari marker classes. The raw +/- prefixes stay in the code and are tokenized by the highlighter's TextMate diff grammar. The block gets theme-colored text via diff scopes (headers, hunks, added/removed lines) but no green/red marker backgrounds or +/- CSS indicators.

Combined with explicit markers

Diff-generated markers are appended to any explicit markers in the meta string. For example, diff lang="go" {1} highlights line 1 as mark in addition to the diff-generated ins/del markers. Standard overlap priority applies: mark < del < ins.

Go API

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html, err := engine.Render(code, kazari.Options{
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    Lang:     "diff",
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    DiffLang: "go",
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    Title:    "changes.go",
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})

DiffLang is available on Options only. It is not part of BlockDefaults or LanguageDefaults and has no config file equivalent.

Configuration

Both the diff language and lang= are required for hybrid mode.

Edge cases

• Without lang=, a diff block renders as plain diff syntax (TextMate grammar) with no Kazari ins/del markers.
• DiffLang is not part of BlockDefaults or LanguageDefaults. Per-language defaults for diff are not possible.
• No config file support for DiffLang.
• Diff-derived markers are added after collapse resolution. Threshold-based collapse preview does not account for diff-derived ins/del lines when computing visible segments.
• Filename comment extraction runs on raw (unstripped) code. A comment on a +/- line (e.g., +// file.go) is not detected as a filename because the prefix blocks the comment-pattern match.
• Diff reuses all marker CSS variables (--kz-ins-bg, --kz-del-bg, --kz-ins-indicator, --kz-del-indicator, etc.). No diff-specific CSS or JS exists.