InDesign GREP and alternatives in a positive lookbehind

When using positive lookbehind (?<=  ... )

such as this...

(?<=open|enter).+

... to get a match on efterything following the words "open" or "enter", I found a small problem with the grep implementation in InDesign (or so I think).

Requiring that either word exists, I find no other solution than to set up two different grep expressions, which is acceptable, but in my eyes not very good:

My example is simplified here.

It seems that the two "alternate" words, need to be the same length, to get a match. And before sending this as a question, I found that Jongware had this in his GREP help:

From http://www.jongware.com/idgrephelp.html

So adding a space after "open ", would get me the right result, since both words are now of the same length:

(?<=open |enter).+

But in my real world scenario that's not possible (since the words are of completely different lengths).

*** Less important extra information about non Adobe GREP starts here ***

On this page: http://caspar.bgsu.edu/~courses/Stats/Labs/Handouts/grepadvanced.htm, I found a piece of text dealing with this exact issue, but according to the text, different lengths of the string are allowed, as long as they all have a fixed length (i.e. no wildcards in side the lookbehind expression):

The contents of a lookbehind assertion are restricted such that all the strings it matches must have a fixed length. However, if there are several alternatives, they do not all have to have the same fixed length. Thus

    (?<=Martin|Lewis)

is permitted [...]

*** Unimportant extra information about non Adobe GREP ends here ***

The author of the caspar.bgsu.edu page above also writes that several assertions can be added one after another:

Several assertions (of any sort) may occur in succession. For example,

    (?<=\d{3})(?<!999)foo

  matches "foo" preceded by three digits that are not "999". Notice that each of the assertions is applied independently at the same point in the subject string.

But I tried that as well, using this GREP with separate assertions for the positive lookbehinds in my example:

(?<=open)(?<=enter).+

... resulting in no match at all:

I don't know what point this is in Jongwares nice GREP flavour of Indesign help file, it might be there, just that I don't know the correct terminology.

Not much of a question this, but perhaps it could be a subject for a discussion anyway. Not the least if my observations are incorret.

Thanks,

Andreas Jansson