Below is included the documentation for this field type from the ISO standard.
5.12 SFVec3f and MFVec3f
The SFVec3f field or event specifies a three-dimensional (3D)
vector. An MFVec3f field or event specifies zero or more 3D
vectors. SFVec3f's and MFVec3f's are written to the VRML file as three
ISO C floating point values (see 2.[ISOC]) separated by
whitespace. For example:
fooVec3f [ 1 42 666, 7 94 0 ]
is an MFVec3f field, fooVec3f, with two valid vectors.
The initial value of an SFVec3f eventOut is (0 0 0). The initial value
of an MFVec3f eventOut is [ ].