diff --git a/src/abstract_tree/command.rs b/src/abstract_tree/command.rs
index 645a29d..d67e7a0 100644
--- a/src/abstract_tree/command.rs
+++ b/src/abstract_tree/command.rs
@@ -4,6 +4,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::{AbstractTree, Error, Format, Map, Result, Type, Value};
 
+/// An external program invokation.
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
 pub struct Command {
     command_text: String,
diff --git a/src/abstract_tree/function_call.rs b/src/abstract_tree/function_call.rs
index b743aca..1839882 100644
--- a/src/abstract_tree/function_call.rs
+++ b/src/abstract_tree/function_call.rs
@@ -5,6 +5,7 @@ use crate::{
     SyntaxPosition, Type, Value,
 };
 
+/// A function being invoked and the arguments it is being passed.
 #[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, PartialOrd, Ord)]
 pub struct FunctionCall {
     function_expression: FunctionExpression,
@@ -13,6 +14,7 @@ pub struct FunctionCall {
 }
 
 impl FunctionCall {
+    /// Returns a new FunctionCall.
     pub fn new(
         function_expression: FunctionExpression,
         arguments: Vec<Expression>,