/^\s*(?:#|$)/

[download]

is the same as 

/^\s*#/ || /^\s*$/

[download]

while 

/^\s*#|$/

[download]

is the same as 

/^\s*#/ || /$/

[download]

In reply to Re: Explain regex ?: usage in grouping by ikegami
in thread Explain regex ?: usage in grouping by plc

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