Lexer Issue with numbers

Hello,

We have the following lexical regex pattern for numbers (int and reals):

(these patterns and look-ahead we are using from the samples)

{Digit}* \. {Digit}+ ([Ee] [\+\-]? {Digit}+)?
{Digit}+ [Ee] [\+\-]? {Digit}+
{Digit}+

When we use the following look-ahead pattern:

{NonWord}|\z

And trying to get tokens with the following code:

graphic 2a

We never get a number token, just a "default" token.

We get the following tokens (ignoring whitespace)

GraphicToken = "graphic"

Default = "2"

Identifier="a"

However, if we remove the look-ahead, we get the following tokens, which seems correct:

GraphicToken = "graphic"

Number = "2"

Identifier="a"

Is this working as intended?  What is the look-ahead actually doing?