Anyone care to explain the construction of this regex.

Note: I know what it does. I am just puzzled as to the benefits of some elements of it's construction. 

(?: 
    (?i) 
    (?: [+-]? ) 
    (?: (?= [0123456789] | [.] )
        (?: [0123456789]* )
        (?: 
            (?: [.] ) 
            (?: [0123456789]{0,} ) 
        )? 
    )
    (?: 
        (?: [E] ) 
        (?: 
            (?: [+-]? )
            (?: [0123456789]+ ) 
        ) 
        | 
    )
)

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In reply to Explain a regex by BrowserUk

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