The parent means here the main code. When you add other designations, they become derivative or daughter codes.
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Main codes
What does all of this mean?

SB (Safety Basic)

The basic safety standard for footwear. These have toe protection against a 200-joule impact. They may also have additional safety features which will be shown via other symbols. For example, if you see SB-P this means that the safety footwear also has the additional feature of Penetration Resistance of the Midsole.

S1

On top of the basic toe protection, S1 ensures the footwear has antistatic protection, is resistant to fuel oil and has energy absorption in the heel. Again other symbols can be added, such as S1-P as above.

S2

S2 has all the same protection as S1, plus the added protection of preventing water penetration and absorption of the upper.

S3

S3 safety footwear encompasses all the same levels of protection as S2, plus midsole penetration resistance.

S4

All the protection offered by S1 but with an entirely moulded polymer/rubber upper (e.g. Wellington Boots) making them waterproof and leak-proof.

S5

All the same features of S4 footwear with the added benefit of midsole penetration resistance.

some additional codes that follow
SRA SRB SRC
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Note added at 5 hrs (2018-03-15 11:59:13 GMT)
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