Support double-square curly braces (#1953)

* Support double-square curly braces

Signed-off-by: ice1000 <ice1000kotlin@foxmail.com>

* Rename `llbrace` to `lBrace`

* Address comments: add mathml

* Fix code style

* Fix doc

* Add to docs/support_table

docs/support_table.md

@@ -527,6 +527,7 @@ table td {
 |\Large|$\Large Large$|`\Large Large`|
 |\LARGE|$\LARGE LARGE$|`\LARGE LARGE`|
 |\LaTeX|$\LaTeX$||
+|\lBrace|$\lBrace$||
 |\lbrace|$\lbrace$||
 |\lbrack|$\lbrack$||
 |\lceil|$\lceil$||
@@ -841,6 +842,7 @@ table td {
 |\Rarr|$\Rarr$||
 |\rArr|$\rArr$||
 |\rarr|$\rarr$||
+|\rBrace|$\rBrace$||
 |\rbrace|$\rbrace$||
 |\rbrack|$\rbrack$||
 |\rceil|$\rceil$||

docs/supported.md

@@ -56,7 +56,7 @@ See also [letters](#letters)
 |$\vert$ <code>&#124;</code> |$\vert$ `\vert` |$┌ ┐$ `┌ ┐`|$\ulcorner \urcorner$ `\ulcorner`<br>$~~~~$`\urcorner`  |$\Downarrow$ `\Downarrow`
 |$\Vert$ <code>&#92;&#124;</code> |$\Vert$ `\Vert` |$└ ┘$ `└ ┘`|$\llcorner \lrcorner$ `\llcorner`<br>$~~~~$`\lrcorner`  |$\Updownarrow$ `\Updownarrow`
 |$\lvert~\rvert$ `\lvert`<br>$~~~~$`\rvert`|$\lVert~\rVert$ `\lVert`<br>$~~~~~$`\rVert` |`\left.`|  `\right.` |$\backslash$ `\backslash`
-|$\lang~\rang$ `\lang`<br>$~~~~$`\rang`|$\lt~\gt$ `\lt \gt`|$⟦~⟧$ `⟦ ⟧`|$\llbracket~\rrbracket$ `\llbracket`<br>$~~~~$`\rrbracket`|
+|$\lang~\rang$ `\lang`<br>$~~~~$`\rang`|$\lt~\gt$ `\lt \gt`|$⟦~⟧$ `⟦ ⟧`|$\llbracket~\rrbracket$ `\llbracket`<br>$~~~~$`\rrbracket`|$\lBrace~\rBrace$ `\lBrace \rBrace`
 
 **Delimiter Sizing**
 

src/macros.js

@@ -849,6 +849,16 @@ defineMacro("\\rrbracket", "\\html@mathml{" +
 defineMacro("\u27e6", "\\llbracket"); // blackboard bold [
 defineMacro("\u27e7", "\\rrbracket"); // blackboard bold ]
 
+defineMacro("\\lBrace", "\\html@mathml{" +
+    "\\mathopen{\\{\\mkern-3.2mu[}}" +
+    "{\\mathopen{\\char`\u2983}}");
+defineMacro("\\rBrace", "\\html@mathml{" +
+    "\\mathclose{]\\mkern-3.2mu\\}}}" +
+    "{\\mathclose{\\char`\u2984}}");
+
+defineMacro("\u2983", "\\lBrace"); // blackboard bold {
+defineMacro("\u2984", "\\rBrace"); // blackboard bold }
+
 // TODO: Create variable sized versions of the last two items. I believe that
 // will require new font glyphs.
 

test/katex-spec.js

@@ -3362,6 +3362,7 @@ describe("Unicode", function() {
         expect`┌x┐ └x┘`.toBuild();
         expect("\u231Cx\u231D \u231Ex\u231F").toBuild();
         expect("\u27E6x\u27E7").toBuild();
+        expect("\\lBrace \\rBrace").toBuild();
     });
 
     it("should build some surrogate pairs", function() {