'What does Regex Index Reference Mean When Referring to Single Quotes

I was playing around with inputting regex patterns in https://regex101.com/ Beginning with the most simple of examples (see screenshot image below) I don't understand the explanation for my pattern '.' (all characters except line terminators) I am assuming that the index values provided are referencing number base terminology. That is 39 base 10, 27 base 16 & 47 base 8?

If I am correct then what is this indexing telling me?

I understand start indexes as used in the following: MathWorks regexp But this particular example, I have posted here, has regex101 referencing the single quote itself.

Perhaps my question is a little esoteric but I would appreciate any suggestions.

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Solution 1:[1]

The quote char ', the ASCII code representation's are either:
39 is decimal, 27 is hex, 47 is octal

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Source: Stack Overflow

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Solution 1 sln