Give a list of elements to be spliced into a surrounding list:

Splice expressions do not automatically flatten inside other heads:

Flatten a list of lists inside another list:

Splice a list of elements inside an expression of a specific head:

Splice a list of elements into another list:

The same object does not splice into expressions with other heads:

Splice a list of elements into an expression with a given head:

The same object does not splice into expressions with other heads:

Splice a list of elements into an expression whose head matches a given pattern:

Splice a list into another list:

Splice[{e₁,e₂,…}] behaves like Sequence[e₁,e₂,…] inside a list:

Sequence objects also splice inside other heads, but not one-argument Splice objects:

Splice[{e₁,e₂,…},_] behaves like Sequence[e₁,e₂,…] under evaluation:

Splice[{}] is equivalent to Nothing:

FlattenAt[list,pos] is equivalent to MapAt[Splice,list,pos]:

Splice may be resolved inside functions with the HoldAll, HoldFirst, and HoldRest attributes:

It is not resolved inside functions with the HoldAllComplete attribute, as this attribute blocks upvalues:

Splice is also not resolved when nested deeply inside a held expression:

Unlike Sequence, the action of Splice cannot be blocked using Unevaluated:

Compare with:

Instead, use Block if it is necessary to temporarily deactivate Splice: