To prevent a GitHub Actions workflow from running when a pull request contains changes only to specific file paths or types, the paths-ignore key is used within the event trigger configuration. The paths-ignore: key (D) defines a filter that accepts a list of patterns. The options - '/.md' (A) and - '/.txt' (B) are the list items specifying the patterns to be ignored. When combined, the workflow trigger is configured to execute for pull requests targeting the main branch, unless all the changed files in the pull request match the ignored patterns (i.e., are .md or .txt files in the root directory).

C. paths:: This key is used to include paths, causing the workflow to run only when specified files change, which is the opposite of the requirement.

E. - 'docs/.md': This pattern is too specific. It only ignores markdown files within the docs directory, failing to meet the broader requirement of ignoring any markdown file.

1. GitHub Docs. (2023). Workflow syntax for GitHub Actions. GitHub. Retrieved from https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#onpullrequestpullrequesttargetpaths-ignore.

Reference Details: The section on.. explicitly states: "When you use paths-ignore, the workflow runs only if at least one file changed is outside of the paths-ignore list." This directly supports the use of paths-ignore: (D) with a list of patterns (A, B) to achieve the desired exclusion.

2. GitHub Docs. (2023). Workflow syntax for GitHub Actions - Filter pattern cheat sheet. GitHub. Retrieved from https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#filter-pattern-cheat-sheet.

Reference Details: This section explains the glob patterns used for path filtering. The pattern .md matches any file with the .md extension in the root directory, confirming the syntax and behavior of options A and B. It also shows that paths and paths-ignore are mutually exclusive alternatives.