NOtes

• Sure: 1) to match any char, use [^] or [\s\S], 2) branch reset group is not supported so use your current approach with a non-capturing group and manipulate the group values upon getting a match.

This works:

(?|(?:([a-z]+):([A-Z]:)((.|\r|\n))^:\2)|([a-z]+):()((?:(?:.|\n|\r)(?!^[a-z]+:))+))

This is decompressed & it works

It needs

• White space removed from values
• Key regex made complete
• Delimiter regex possibly allow different characters
• port to work on all regex engines

(?| # Match everything,

(?: # Non-Capture Match delimited key/value pairs, 

    ([a-z]+): # Key, Capture Group #1
        ([A-Z]*:) # Delimiter, Capture Group #2
    ( # Match everything after the delimiter
        (.|\r|\n)*  # Value, Capture Group #3
    )
    ^:\2   # Delimiter, ending value capture

)

| (?: # Match non-delimited values ([a-z]+): # Key, Capture Group #1 () # Capture Group #2, absense of delimiter ( # Value, Capture Group #3 (?: (?:.|\n|\r) (?!^[a-z]+:) # look ahead to make sure there is NOT a key )+

    )
)

)

This is a work-in-progress

Working on:

• DONE-- Replace (.|\r|\n)* with (?s).*

• White space removed from values

  • NEW LINES at beginning are removed
  • Need to remove new lines at the end

• Key regex made complete

• Delimiter regex possibly allow different characters (?s) (?| # Balance the capture groups

  (?: # Non-Capture Match delimited key/value pairs,

    ([a-z]+): # Key, Capture Group #1
        ([A-Z]*:) # Delimiter, Capture Group #2
    \s*
    ( # Match everything after the delimiter, Capture Group #3
        (?:
            .  # Value, Capture Group #3
            (?!\s+:\2) # Do NOT match trailing white space
        )*
    )
    \s* # Match the trailing white space
    ^:\2   # Delimiter, ending value capture
  

  )

| (?: # Match non-delimited values ([a-z]+): # Key, Capture Group #1 () # Capture Group #2, absense of delimiter \s* ( # Value, Capture Group #3 (?: . (?!^[a-z]+:) # look ahead to make sure there is NOT a key )+

    )
)

)

Non-delimited values only

([a-z]+):((?:(?:.|\n|\r)(?!^[a-z]+:(?![A-Z]*:)))+)