Add crate private opcode and other constants

diff --git a/primitives/src/opcodes.rs b/primitives/src/opcodes.rs
index d4d8be09..1c94a080 100644
--- a/primitives/src/opcodes.rs
+++ b/primitives/src/opcodes.rs
@@ -166,6 +166,18 @@ pub(crate) const OP_PUSHDATA4: u8 = 0x4e;
 /// Push an empty array onto the stack.
 pub(crate) const OP_PUSHBYTES_0: Opcode = Opcode::from_u8(0x00);
 
+/// Push the next 2 bytes as an array onto the stack.
+#[cfg(feature = "alloc")]
+pub(crate) const OP_PUSHBYTES_2: Opcode = Opcode::from_u8(0x02);
+
+/// Push the next 20 bytes as an array onto the stack.
+#[cfg(feature = "alloc")]
+pub(crate) const OP_PUSHBYTES_20: Opcode = Opcode::from_u8(0x14);
+
+/// Push the next 32 bytes as an array onto the stack.
+#[cfg(feature = "alloc")]
+pub(crate) const OP_PUSHBYTES_32: Opcode = Opcode::from_u8(0x20);
+
 /// Format a byte as a script opcode.
 #[cfg(feature = "alloc")]
 pub(crate) fn fmt_opcode(op: u8, f: &mut fmt::Formatter) -> fmt::Result {
diff --git a/primitives/src/script/mod.rs b/primitives/src/script/mod.rs
index b71692d7..cb9f4f0a 100644
--- a/primitives/src/script/mod.rs
+++ b/primitives/src/script/mod.rs
@@ -90,6 +90,9 @@ pub const MAX_REDEEM_SCRIPT_SIZE: usize = 520;
 /// The maximum allowed redeem script size of the witness script.
 pub const MAX_WITNESS_SCRIPT_SIZE: usize = 10_000;
 
+/// The P2A program which is given by 0x4e73.
+pub(crate) const P2A_PROGRAM: [u8; 2] = [78, 115];
+
 /// Generates P2WSH-type of scriptPubkey with a given [`WitnessVersion`] and the program bytes.
 /// Does not do any checks on version or program length.
 ///