Add \QuartoMarkdownBase64{} in advanced docs

Author: cwickham

docs/advanced/latex-raw.qmd

@@ -0,0 +1,19 @@
+---
+title: Include Quarto Markdown in LaTeX Raw Blocks
+summary: Allows library authors to emit raw blocks that include Quarto features like cross-references or shortcodes.
+---
+
+Use the syntax `\QuartoMarkdownBase64{<<base64-encoded-markdown-content>>}` 
+to include Quarto Markdown in LaTeX raw blocks. 
+When this syntax is detected by Quarto, the contents will be decoded, 
+processed in Quarto (including user filters), and then inserted back into the LaTeX raw block.
+This allows libraries that emit raw blocks to benefit
+from Quarto features such as cross-reference resolution and shortcodes.
+
+This is useful for third-party libraries that seek to emit LaTeX content that nevertheless 
+can have "quarto content". Note that, unlike the [equivalent HTML feature](/docs/authoring/tables.qmd#html-tables), 
+Quarto currently only supports base-64 encoded content in LaTeX blocks.
+
+This LaTeX feature cannot currently be disabled.
+We expect this to not be necessary because `QuartoMarkdownBase64` is unlikely to conflict with
+existing LaTeX environments.