diff --git a/packages/common/http/src/headers.ts b/packages/common/http/src/headers.ts
index c8ee642e49..3e1a5222ad 100755
--- a/packages/common/http/src/headers.ts
+++ b/packages/common/http/src/headers.ts
@@ -14,8 +14,8 @@ interface Update {
 
 /**
  * Represents the header configuration options for an HTTP request.
- *
- * Instances should be assumed immutable with lazy parsing.
+ * Instances are immutable. Modifying methods return a cloned
+ * instance with the change. The original object is never changed.
  *
  * @publicApi
  */
@@ -85,11 +85,11 @@ export class HttpHeaders {
   }
 
   /**
-   * Checks for existence of a header by a given name.
+   * Checks for existence of a given header.
    *
    * @param name The header name to check for existence.
    *
-   * @returns Whether the header exits.
+   * @returns True if the header exists, false otherwise.
    */
   has(name: string): boolean {
     this.init();
@@ -98,11 +98,11 @@ export class HttpHeaders {
   }
 
   /**
-   * Retrieves the first header value that matches a given name.
+   * Retrieves the first value of a given header.
    *
-   * @param name The header name to retrieve.
+   * @param name The header name.
    *
-   * @returns A string if the header exists, null otherwise
+   * @returns The value string if the header exists, null otherwise
    */
   get(name: string): string|null {
     this.init();
@@ -123,9 +123,9 @@ export class HttpHeaders {
   }
 
   /**
-   * Retrieves a list of header values for a given header name.
+   * Retrieves a list of values for a given header.
    *
-   * @param name The header name from which to retrieve the values.
+   * @param name The header name from which to retrieve values.
    *
    * @returns A string of values if the header exists, null otherwise.
    */
@@ -136,36 +136,38 @@ export class HttpHeaders {
   }
 
   /**
-   * Appends a new header value to the existing set of
-   * header values.
+   * Appends a new value to the existing set of values for a header
+   * and returns them in a clone of the original instance.
    *
-   * @param name The header name for which to append the values.
+   * @param name The header name for which to append the value or values.
+   * @param value The new value or array of values.
    *
-   * @returns A clone of the HTTP header object with the value appended.
+   * @returns A clone of the HTTP headers object with the value appended to the given header.
    */
 
   append(name: string, value: string|string[]): HttpHeaders {
     return this.clone({name, value, op: 'a'});
   }
   /**
-   * Sets a header value for a given name. If the header name already exists,
-   * its value is replaced with the given value.
+   * Sets or modifies a value for a given header in a clone of the original instance.
+   * If the header already exists, its value is replaced with the given value
+   * in the returned object.
    *
    * @param name The header name.
-   * @param value The value to set or overide for a given name.
+   * @param value The value or values to set or overide for the given header.
    *
-   * @returns A clone of the HTTP header object with the newly set header value.
+   * @returns A clone of the HTTP headers object with the newly set header value.
    */
   set(name: string, value: string|string[]): HttpHeaders {
     return this.clone({name, value, op: 's'});
   }
   /**
-   * Deletes all header values for a given name.
+   * Deletes values for a given header in a clone of the original instance.
    *
    * @param name The header name.
-   * @param value The header values to delete for a given name.
+   * @param value The value or values to delete for the given header.
    *
-   * @returns A clone of the HTTP header object.
+   * @returns A clone of the HTTP headers object with the given value deleted.
    */
   delete (name: string, value?: string|string[]): HttpHeaders {
     return this.clone({name, value, op: 'd'});