docs: state the validation status and correct claims the material contradicts

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docs/man/gasm-lint.1

@@ -33,7 +33,11 @@ The function can fall off its end without a terminator.
 TEXT flags are used without including textflag.h.
 .TP
 .B abi-argsize
-The declared frame or argument size disagrees with the
+The declared argument area (the
+.I \-args
+part of
+.IR $frame\-args )
+disagrees with the
 .B //\ function
 signature.
 .TP
@@ -52,7 +56,8 @@ FUNCDATA and PCDATA indices are malformed.
 A label no jump reaches.
 .TP
 .B invalid-textflag
-A TEXT flag combination the toolchain rejects.
+An unknown TEXT or GLOBL flag, reported one flag at a time; numeric flags
+are accepted as textflag.h constants.
 .TP
 .B stack-imbalance
 The function does not restore the stack pointer on every path.
@@ -61,11 +66,18 @@ The function does not restore the stack pointer on every path.
 An operand register has the wrong width for the instruction.
 .TP
 .B abi0-register-args
-A call passes arguments in registers where ABI0 expects the stack
-frame.
+A function whose
+.B //\ function
+parameters are never read from their
+.IR name+offset(FP)
+frame slots, which usually means the body takes its arguments from
+registers instead.
 .TP
 .B nonportable-register-name
-A register spelling that does not exist on the target architecture.
+An amd64 register alias gasm accepts but
+.B go tool asm
+rejects (the RAX/EAX family); the canonical spelling is named in the
+diagnostic.
 .TP
 .B unencodable-instruction
 The mnemonic is known to the table but the encoder cannot assemble it