feat: scope highlight for html tags

## Details

Request: #528

Adds an optional `scope_highlight` value that can be set for individual
html tags which will be applied as the highlight group around the body
of a tag's content.

As part of this change all existing fields of html tags have been made
optional, meaning `icon` and `highlight` are no longer required. In
order to render an icon both `icon` and `highlight` are required,
specifying one without the other will not cause errors, but will result
in no icon being shown so really does not make sense to do.

Similarly specifying no values for a tag will not cause errors, but will
result in no rendering so also does not make sense to do.

Author: MeanderingProgrammer

README.md

@@ -853,8 +853,9 @@ require('render-markdown').setup({
         },
         -- HTML tags whose start and end will be hidden and icon shown.
         -- The key is matched against the tag name, value type below.
-        -- | icon      | gets inlined at the start |
-        -- | highlight | highlight for the icon    |
+        -- | icon            | optional icon inlined at start of tag           |
+        -- | highlight       | optional highlight for the icon                 |
+        -- | scope_highlight | optional highlight for item associated with tag |
         tag = {},
     },
     win_options = {

doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*      For NVIM v0.11.4     Last change: 2025 September 17
+*render-markdown.txt*      For NVIM v0.11.4     Last change: 2025 September 22
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*
@@ -915,8 +915,9 @@ Default Configuration ~
             },
             -- HTML tags whose start and end will be hidden and icon shown.
             -- The key is matched against the tag name, value type below.
-            -- | icon      | gets inlined at the start |
-            -- | highlight | highlight for the icon    |
+            -- | icon            | optional icon inlined at start of tag           |
+            -- | highlight       | optional highlight for the icon                 |
+            -- | scope_highlight | optional highlight for item associated with tag |
             tag = {},
         },
         win_options = {

lua/render-markdown/config/html.lua

@@ -8,8 +8,9 @@
 ---@field highlight string
 
 ---@class (exact) render.md.html.Tag
----@field icon string
----@field highlight string
+---@field icon? string
+---@field highlight? string
+---@field scope_highlight? string
 
 ---@class render.md.html.Cfg
 local M = {}
@@ -30,8 +31,9 @@ M.default = {
     },
     -- HTML tags whose start and end will be hidden and icon shown.
     -- The key is matched against the tag name, value type below.
-    -- | icon      | gets inlined at the start |
-    -- | highlight | highlight for the icon    |
+    -- | icon            | optional icon inlined at start of tag           |
+    -- | highlight       | optional highlight for the icon                 |
+    -- | scope_highlight | optional highlight for item associated with tag |
     tag = {},
 }
 
@@ -40,8 +42,9 @@ function M.schema()
     ---@type render.md.Schema
     local tag = {
         record = {
-            icon = { type = 'string' },
-            highlight = { type = 'string' },
+            icon = { optional = true, type = 'string' },
+            highlight = { optional = true, type = 'string' },
+            scope_highlight = { optional = true, type = 'string' },
         },
     }
     return require('render-markdown.config.base').schema({

lua/render-markdown/health.lua

@@ -6,7 +6,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '8.8.9'
+M.version = '8.8.10'
 
 function M.check()
     M.start('versions')

lua/render-markdown/render/html/tag.lua

@@ -21,12 +21,30 @@ function Render:run()
     if not config then
         return
     end
+
     self.marks:over(self.config, true, start_tag, { conceal = '' })
     self.marks:over(self.config, true, end_tag, { conceal = '' })
-    self.marks:start(self.config, false, self.node, {
-        virt_text = { { config.icon, config.highlight } },
-        virt_text_pos = 'inline',
-    })
+
+    local icon, highlight = config.icon, config.highlight
+    if icon and highlight then
+        self.marks:start(self.config, false, self.node, {
+            virt_text = { { icon, highlight } },
+            virt_text_pos = 'inline',
+        })
+    end
+
+    local scope_highlight = config.scope_highlight
+    local start_row = start_tag and start_tag.end_row or self.node.start_row
+    local start_col = start_tag and start_tag.end_col or self.node.start_col
+    local end_row = end_tag and end_tag.start_row or self.node.end_row
+    local end_col = end_tag and end_tag.start_col or self.node.end_col
+    if scope_highlight then
+        self.marks:add(self.config, true, start_row, start_col, {
+            end_row = end_row,
+            end_col = end_col,
+            hl_group = scope_highlight,
+        })
+    end
 end
 
 return Render