'Are standard conversion sequences include explicit conversions?

I am just trying to understand what does the standard mean by "standard conversion sequences"; and I have ended up with that "standard conversion sequences" are "sequences of standard implicit conversions". But I think that's not true for some contexts; for instance, from [expr.static.cast]/7:

[..] A program is ill-formed if it uses static_­cast to perform the inverse of an ill-formed standard conversion sequence.

struct B { };
struct D : private B { };
void f() {
  static_cast<D*>((B*)0);  // error: B is a private base of D
  // ..
}

And General[conv.general]/1 states:

Standard conversions are implicit conversions with built-in meaning. [..] A standard conversion sequence is a sequence of standard conversions in the following order:

  • [..]
  • (1.2) Zero or one conversion from the following set: integral promotions, floating-point promotion, integral conversions, floating-point conversions, floating-integral conversions, pointer conversions, pointer-to-member conversions, and boolean conversions.
  • [..]

As I know, I think that a standard conversion sequence is only implicit conversions not including any explicit conversion. I mean the above conversion (B*)0 is explicit pointer conversion, even though the standard said that this conversion is ill-formed standard conversion sequance.

So if my thinking is true, why is this explicit cast expression (B*)0 is said to be standard conversion sequence and it is an implicit conversion not explicit?

From this answer on a some question:

the standard conversion is a set of built-in rules the compiler can apply when converting one type to another. Those built-in conversions include:

  • No conversions
  • Lvalue-to-rvalue conversion
  • Array-to-pointer conversion
  • Function-to-pointer conversion
  • Qualification conversions
  • Integral promotions
  • Floating point promotion
  • Integral conversions
  • Floating point conversions
  • Floating-integral conversions
  • Pointer conversions
  • Pointer to member conversions
  • Boolean conversions

Given the conversions above, if those conversions are performed explicitly, do they still said to be standard conversion sequences?

In general, Are conversions performed explicitly (including C++ cast operators) said to be standard conversion sequences?

c++implicit-conversion


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