a$)$ BS EN $1993-1-1$ classified the steel cross$-$section into four classes.

Class $1-$ Cross$-$sections can form a plastic hinge with the rotation capacity required from plastic analysis without reducing the resistance.

Class $2-$ Cross$-$sections arc those that can develop their plastic moment resistance but have limited rotation capacity because of local buckling.

Class $3-$ Cross$-$sections are those in which the stress in the extreme compression fibre of the steel member assuming an elastic distribution of stresses can reach the yield strength. Still, local buckling is liable to prevent development of plastic moment resistance.

Class $4-$ Cross$-$sections are those in which local buckling will occur before the attainment of yield stress in one or more parts of the cross$-$section.

What is the role of this cross$-$section classification?