In function main() in manual/Init-and-Destroy-Functions.html, the call to yylex() should be yylex(scanner)
This is fixed in the flex codebase. I am having an issue generating the html to publish on the flex web site, however. I'll get the updated version posted after I have resolved the html generation issue.
I resolved the issue with generating the html and have uploaded the corrected manual to the flex web site.