A vim syntax definition file for lexc is presented on the following wiki page: Syntax highlighting in Vim. This plugin works in that it highlights syntax nicely, but it doesn't seem to allow folding (i.e., collapsing of sections). Modify or rewrite the plugin so that it supports folding of Multichar_Symbols and LEXICON blocks.
For further information and guidance on this task, you are encouraged to come to our IRC channel.