diff --git a/fish-rust/src/lib.rs b/fish-rust/src/lib.rs
index 1ded44959..bd0c00d13 100644
--- a/fish-rust/src/lib.rs
+++ b/fish-rust/src/lib.rs
@@ -45,6 +45,7 @@ mod operation_context;
 mod parse_constants;
 mod parse_tree;
 mod parse_util;
+mod parser_keywords;
 mod path;
 mod re;
 mod redirection;
diff --git a/fish-rust/src/parser_keywords.rs b/fish-rust/src/parser_keywords.rs
new file mode 100644
index 000000000..2b870e494
--- /dev/null
+++ b/fish-rust/src/parser_keywords.rs
@@ -0,0 +1,54 @@
+//! Functions having to do with parser keywords, like testing if a function is a block command.
+
+use crate::wchar::wstr;
+use widestring_suffix::widestrs;
+
+#[widestrs]
+const SKIP_KEYWORDS: &[&wstr] = &["else"L, "begin"L];
+#[widestrs]
+const SUBCOMMAND_KEYWORDS: &[&wstr] = &[
+    "command"L, "builtin"L, "while"L, "exec"L, "if"L, "and"L, "or"L, "not"L, "time"L, "begin"L,
+];
+#[widestrs]
+const BLOCK_KEYWORDS: &[&wstr] = &["for"L, "while"L, "if"L, "function"L, "switch"L, "begin"L];
+
+// Don't forget to add any new reserved keywords to the documentation
+#[widestrs]
+const RESERVED_KEYWORDS: &[&wstr] = &[
+    "end"L,
+    "case"L,
+    "else"L,
+    "return"L,
+    "continue"L,
+    "break"L,
+    "argparse"L,
+    "read"L,
+    "string"L,
+    "set"L,
+    "status"L,
+    "test"L,
+    "["L,
+    "_"L,
+    "eval"L,
+];
+
+// The lists above are purposely implemented separately from the logic below, so that future
+// maintainers may assume the contents of the list based off their names, and not off what the
+// functions below require them to contain.
+
+/// Tests if the specified commands parameters should be interpreted as another command, which will
+/// be true if the command is either 'command', 'exec', 'if', 'while', or 'builtin'.  This does not
+/// handle "else if" which is more complicated.
+pub fn parser_keywords_is_subcommand(cmd: &wstr) -> bool {
+    SUBCOMMAND_KEYWORDS.contains(&cmd) || SKIP_KEYWORDS.contains(&cmd)
+}
+
+/// Tests if the specified command is a reserved word, i.e. if it is the name of one of the builtin
+/// functions that change the block or command scope, like 'for', 'end' or 'command' or 'exec'.
+/// These functions may not be overloaded, so their names are reserved.
+pub fn parser_keywords_is_reserved(word: &wstr) -> bool {
+    SUBCOMMAND_KEYWORDS.contains(&word)
+        || SKIP_KEYWORDS.contains(&word)
+        || BLOCK_KEYWORDS.contains(&word)
+        || RESERVED_KEYWORDS.contains(&word)
+}