some bad numbers follow:

1.+2
5.5ea
5.5e-x

valid:
+ - * / % ** ( ) = < > : , . ' " </
+-*/%**()=<>:,.'"</

there are thee invalid characters here:

abc$def!ghi&xyz

numbers123between1.1words
<tag
< notAtag

<!-- this is a comment
-->

<!- this is not, in fact there is an
invalid character
-->

unterminated comment coming...

<!-- i wonder how you will handle this ...
-