Add dependency on jsregexp to doc+readme.

DOC.md

@@ -1093,6 +1093,8 @@ tabstop/placeholder/choice which will be visited just before the new `$0`. This
 new `$0` will be inserted at the (textually) earliest valid position behind the
 invalid `$0`.
 
+## Snipmate
+
 It is furthermore possible to parse snipmate-snippets (this includes support for
 vimscript-evaluation!!)  
 Snipmate-snippets have to be parsed with a different function,
@@ -1101,6 +1103,25 @@ Snipmate-snippets have to be parsed with a different function,
 ls.parser.parse_snipmate("year", "The year is `strftime('%Y')`")
 ```
 
+`parse_snipmate` is the same as `parse_snippet`, only the snippet-body is parsed
+differently.
+
+## Transformations
+
+To apply
+[Variable/Placeholder-transformations](https://code.visualstudio.com/docs/editor/userdefinedsnippets#_variable-transforms),
+luasnip needs to apply ECMAScrip-regexes.  
+This is implemented by relying on [`jsregexp`](https://github.com/kmarius/jsregexp).  
+`jsregexp` is available as a luarock, and, as such, can be installed by
+`packer.nvim` (although actual usage may require a small workaround, see
+[here](https://github.com/wbthomason/packer.nvim/issues/593) or
+[here](https://github.com/wbthomason/packer.nvim/issues/358)).  
+Alternatively, the repo can be cloned, `make`d, and the resulting `jsregexp.so`
+placed in some place where nvim can find it (probably `~/.config/nvim/lua/`).
+
+If `jsregexp` cannot be found, luasnip and omits the transformation and just
+inserts the input.
+
 # VARIABLES
 
 All `TM_something`-variables are supported with two additions:

README.md

@@ -21,10 +21,10 @@ https://user-images.githubusercontent.com/41961280/122515860-5179fa00-d00e-11eb-
 
 # Drawbacks
 - Snippets that make use of the entire functionality of this plugin have to be defined in Lua (but 95% of snippets can be written in lsp-syntax).
-- The LSP-parser does not support Regex-Transformations.
 
 # Requirements
 Neovim >= 0.5 (extmarks)
+`jsregexp` for lsp-snippet-transformations.
 
 # Setup
 ## Install