diff --git a/src/APIHandler.py b/src/APIHandler.py
index d8701a9..65c67c3 100644
--- a/src/APIHandler.py
+++ b/src/APIHandler.py
@@ -4,7 +4,18 @@ import elabapi_python as elabapi
 
 class APIHandler:
     """
-    Class to standardize the format of the headers of our http requests.
+    Class which handles all interactions with the eLabFTW API.
+    It provides methods to retrieve data from the API and download attachments.
+    It relies minimally on the elabapi-python library, which is used only for downloading attachments
+    (since the API doesn't support downloading attachments AFAIK).
+
+    Args:
+        api_key:          A valid API key for the eLabFTW instance where the data is stored, with permissions to access the relevant entries.
+                          eLabFTW's API keys are well documented here: https://doc.elabftw.net/docs/usage/api/.
+                          If you don't have an API key and are uncapable of creating one, contact your eLabFTW administrator.
+                          Or RTFM and create one yourself, it's not that hard.
+        ELABFTW_API_URL:  Complete URL of the eLabFTW instance's root for the API endpoints.
+                          In full caps because it won't (shouldn't) be changed much.
     """
 
     # TO-DO: remove static url.
@@ -20,40 +31,54 @@ class APIHandler:
 
     def get_entry_from_elabid(self, elabid, entryType="items"):
         """
-        Method which returns a resource's raw data (as dictionary) from its elabid and entry type.
+        Returns raw data (as dictionary) from its elabid and entry type.
 
-        Entry type can be either "experiments" or "items".
+        args:
+            elabid:     elabftw internal id of the selected resource.
+            entryType:  Resource type. Anything other than "experiments" or "items" WILL raise an error.
         """
-        # TO-DO: validation and error handling on entryType value.
+        if entryType not in ["experiments", "items"]:
+            raise Exception(
+                "You can only download attachments from experiments or items."
+            )
+
         header = self.header
         response = requests.get(
             headers=header, url=f"{self.elaburl}/{entryType}/{elabid}", verify=True
         )
-        if response.status_code // 100 in [1, 2, 3]:
-            entry_data = response.json()
-            return entry_data
-        elif response.status_code // 100 == 4:
+
+        # Response is 5xx = server error:
+        if response.status_code // 100 == 5:
+            raise ConnectionError(
+                f"There's a problem on the server. Status code: {response.status_code}."
+            )
+
+        # Response is 4xx = client error:
+        if response.status_code // 100 == 4:
             match response.status_code:
                 case 401 | 403:
+                    # Forbidden or unauthorized:
                     raise ConnectionError(
                         f"Invalid API key, authentication method or elabid. Check if an item with ID = {elabid} actually exists."
                     )
                 case 404:
+                    # Lapalissian:
                     raise ConnectionError(
                         f"404: Not Found. This means there's no resource with this elabid (wrong elabid?) on your eLabFTW (wrong endpoint?)."
                     )
                 case 400:
+                    # I genuinely have no idea:
                     raise ConnectionError(
                         f"400: Bad Request. This means the API endpoint you tried to reach is invalid. Did you tamper with the source code? If not, contact the developer."
                     )
                 case _:
+                    # For some fucking reason, this is the only error I actually get from the API...
                     raise ConnectionError(
                         f"HTTP request failed with status code: {response.status_code} (NOTE: 4xx means user's fault)."
                     )
-        else:
-            raise ConnectionError(
-                f"There's a problem on the server. Status code: {response.status_code}."
-            )
+
+        entry_data = response.json()
+        return entry_data
 
     def download_attachments_data(self, elabid, entryType="experiments"):
         """
@@ -123,4 +148,3 @@ class APIHandler:
             with open(os.path.join(dump_dir, f"exp{elabid}-{file}"), "wb") as f:
                 f.write(raw_data)
         return
-