diff --git a/.gitignore b/.gitignore
index b1f138d..e2422b5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,15 +1,15 @@
-.idea
+__pycache__
+*/output/
+*/ignored/
+*.egg-info/
+.idea/
+build/
 dev/
+dist/
 env/
-__pycache__
-*.pyc
 *~$*
+*.pyc
 *.DS_Store
-dist/
-build/
-MANIFEST
-tags
 *.swp
-/*.html
-*.egg-info
-output/
+tags
+MANIFEST
diff --git a/CHANGES.txt b/CHANGES.txt
index 6464d54..9391fea 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,3 +1,7 @@
+v0.5.0, 24 January 2019
+ * XlsForm now has a warnings attribute
+ * Updated requirements: requirements-unlock.txt list base, non-transitive depdendencies, while requirements.txt lists the results of pip freeze.
+
 v0.4.0, 12 December 2018
  * Added direct python API for borrow, e.g. from pmix.borrow import borrow.
 
diff --git a/makefile b/makefile
index a9fba79..42fc2b3 100644
--- a/makefile
+++ b/makefile
@@ -75,6 +75,9 @@ clean:
 	rm -rf ./*.egg-info
 build: clean
 	python3 setup.py sdist bdist_wheel
+install:
+	pip install -r requirements-unlocked.txt --no-cache-dir; \
+	pip freeze > requirements.txt
 pypi: build
 	twine upload --repository-url https://upload.pypi.org/legacy/ dist/*;
 pypi_test: build
diff --git a/pmix/__init__.py b/pmix/__init__.py
index 35c3c92..24de8ce 100644
--- a/pmix/__init__.py
+++ b/pmix/__init__.py
@@ -1 +1,2 @@
 """A mixed bag of utilities for PMA2020."""
+
diff --git a/pmix/__version__.py b/pmix/__version__.py
index 058fbca..4c97a37 100644
--- a/pmix/__version__.py
+++ b/pmix/__version__.py
@@ -1,3 +1,3 @@
 """Semantic versioning for the package pmix."""
-VERSION = (0, 4, 0)
+VERSION = (0, 5, 0)
 __version__ = '.'.join(map(str, VERSION))
diff --git a/pmix/cell.py b/pmix/cell.py
index 14f7c67..25ce941 100644
--- a/pmix/cell.py
+++ b/pmix/cell.py
@@ -44,6 +44,10 @@ class Cell:
     def __init__(self, value=None):
         """Initialize cell to have value as Python object.
 
+        Attributes:
+            value: A python object that is stored in the cell. Should be
+                castable as str.
+
         Args:
             value: The value of the cell. Defaults to None for a blank cell.
         """
diff --git a/pmix/workbook.py b/pmix/workbook.py
index d63fd75..c5edc42 100644
--- a/pmix/workbook.py
+++ b/pmix/workbook.py
@@ -1,5 +1,4 @@
 """Module defines a Workbook class to represent Excel files."""
-
 import itertools
 import copy
 import os.path
diff --git a/pmix/xlsform.py b/pmix/xlsform.py
index c24eb4f..0de0a91 100644
--- a/pmix/xlsform.py
+++ b/pmix/xlsform.py
@@ -1,4 +1,6 @@
 """Module defining Xlsform class to work with ODK XLSForms."""
+from copy import deepcopy
+from xlsxwriter.utility import xl_col_to_name
 from typing import List, Optional
 
 from pmix.xlstab import Xlstab
@@ -26,6 +28,8 @@ def __init__(self, path: str, stripstr: bool = True):
         self.data = [Xlstab.from_worksheet(ws) for ws in self]
         self.settings = {}
         self.init_settings()
+        self.warnings = {}
+        self.init_warnings()
 
     def init_settings(self):
         """Get settings from Xlsform.
@@ -86,6 +90,44 @@ def form_language(self) -> Optional[str]:
                 pass
         return language
 
+    def init_warnings(self):
+        """Validate data and return warnings.
+
+        Side effects:
+            self.warnings (dict): sets warnings
+
+        Examples:
+            self.warnings =
+            '#VALUE!': {
+                'survey': [X10, C56, E122]
+            },
+            '#REF!': {
+                'survey': [T5, C53]
+            },
+        }
+        """
+        warnings_schema = {  # taken from xlrd.error_text_from_code
+            '#NULL!': {},  # Intersection of two cell ranges is empty
+            '#DIV/0': {},  # Division by zero
+            '#VALUE!': {},  # Wrong type of operand
+            '#REF!': {},  # Illegal or deleted cell reference
+            '#NAME?': {},  # Wrong function or range name
+            '#NUM!': {},  # Value range overflow
+            '#N/A': {},  # Argument or function not available
+        }
+        warnings = deepcopy(warnings_schema)
+        error_codes = [k for k, v in warnings.items()]
+        for ws in self.data:
+            for i, row in enumerate(ws.data):
+                for j, cell in enumerate(row):
+                    if cell.value in error_codes:
+                        if ws.name not in warnings[cell.value]:
+                            warnings[cell.value][ws.name] = []
+                        label = xl_col_to_name(j)
+                        warnings[cell.value][ws.name].append(label + str(i))
+        warnings = {k: v for k, v in warnings.items() if v != {}}
+        self.warnings = warnings
+
     def add_language(self, language: str):
         """Add appropriate language columns to an Xlsform.
 
diff --git a/requirements-dev.txt b/requirements-unlocked.txt
similarity index 100%
rename from requirements-dev.txt
rename to requirements-unlocked.txt
diff --git a/setup.py b/setup.py
index 4ac906b..14a7900 100644
--- a/setup.py
+++ b/setup.py
@@ -65,12 +65,15 @@ def status(s):
         print('\033[1m{0}\033[0m'.format(s))
 
     def initialize_options(self):
+        """Initialize options"""
         pass
 
     def finalize_options(self):
+        """Finalize options"""
         pass
 
     def run(self):
+        """Run"""
         try:
             self.status('Removing previous builds…')
             rmtree(os.path.join(here, 'dist'))
@@ -78,8 +81,8 @@ def run(self):
             pass
 
         self.status('Building Source and Wheel (universal) distribution…')
-        os.system(
-            '{0} setup.py sdist bdist_wheel --universal'.format(sys.executable))
+        os.system('{0} setup.py sdist bdist_wheel --universal'
+                  .format(sys.executable))
 
         self.status('Uploading the package to PyPI via Twine…')
         os.system('twine upload dist/*')