---------------
+Declaration
+^^^^^^^^^^^
+
+
+Declares a register that is will be referenced as an operand in Instruction
+tokens.
+
+File field contains register file that is being declared and is one
+of TGSI_FILE.
+
+UsageMask field specifies which of the register components can be accessed
+and is one of TGSI_WRITEMASK.
+
+Interpolate field is only valid for fragment shader INPUT register files.
+It specifes the way input is being interpolated by the rasteriser and is one
+of TGSI_INTERPOLATE.
+
+If Dimension flag is set to 1, a Declaration Dimension token follows.
+
+If Semantic flag is set to 1, a Declaration Semantic token follows.
+
+CylindricalWrap bitfield is only valid for fragment shader INPUT register
+files. It specifies which register components should be subject to cylindrical
+wrapping when interpolating by the rasteriser. If TGSI_CYLINDRICAL_WRAP_X
+is set to 1, the X component should be interpolated according to cylindrical
+wrapping rules.
+
+
Declaration Semantic
^^^^^^^^^^^^^^^^^^^^^^^^
"""""""""""""""""""
PSIZE, or point size, is used to specify point sizes per-vertex. It should
-be in ``(p, n, x, f)`` format, where ``p`` is the point size, ``n`` is the minimum
-size, ``x`` is the maximum size, and ``f`` is the fade threshold.
-
-XXX this is arb_vp. is this what we actually do? should double-check...
+be in ``(s, 0, 0, 1)`` format, where ``s`` is the (possibly clamped) point size.
+Only the first component matters when writing from the vertex shader.
When using this semantic, be sure to set the appropriate state in the
:ref:`rasterizer` first.