Builds on #227 and #317.

Summary

This PR introduces first-class support for Word Alt Text in python-docx. Users can now set and read both the Alt Text Title and Alt Text Description (as shown in Word’s Accessibility pane) directly through the API when inserting or editing pictures.

Motive

Previously, python-docx did not expose a clean API for working with image alternative text. Users had to manually manipulate XML to set or retrieve <wp:docPr> attributes (title, descr). This enhancement improves accessibility workflows and enables automated tools (e.g., alt-text generators) to embed compliant descriptions directly into Word documents.

Implementation

• CT_NonVisualDrawingProps (oxml/shape.py): Added optional attributes title and descr.
• CT_Inline.new() / new_pic_inline(): Accept and apply title / descr to <wp:docPr>.
• StoryPart.new_pic_inline(): Added title and descr parameters and forwarded them to CT_Inline.new_pic_inline().
• Run.add_picture() and Document.add_picture(): Updated to accept and pass through title and descr for inline pictures.
• InlineShape (shape.py): Added new alt_text and alt_title properties for convenient read/write access to docPr.descr and docPr.title.

Usage Examples

from docx import Document
from docx.shared import Inches

doc = Document()

# Insert an image with alt text
doc.add_picture(
    "chart.png",
    width=Inches(5),
    descr="Line chart showing sales growth from 2020 to 2024.",
    title="Sales Growth Chart"
)

# Access or modify alt text of an existing shape
shape = doc.inline_shapes[0]
print(shape.alt_text)      # "Line chart showing sales growth from 2020 to 2024."
shape.alt_text = "Updated alt text description."
shape.alt_title = "Updated title."
doc.save("report_with_alt_text.docx")

Additional Notes

• Verified functionality using a test script that inserted an image, saved, reloaded, and confirmed alt_title and alt_text persisted correctly.
• No breaking API changes; title and descr are optional.
• Works across all story parts (document, headers, footers).
• Backwards compatible with existing documents.
• Enables accessibility tooling, automated captioning, and alt-text validation in Word documents.