diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 4a59a59801..b096cf4108 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -56,7 +56,7 @@ jobs:
             using Pkg
             Pkg.instantiate()
             Pkg.develop(PackageSpec(path=pwd()))
-            Pkg.add(["IOCapture", "DocumenterMarkdown", "tectonic_jll"])'
+            Pkg.add(["IOCapture", "tectonic_jll"])'
       - run: julia --project=test/examples --code-coverage test/examples/tests_latex.jl
       - uses: julia-actions/julia-processcoverage@v1
       - uses: codecov/codecov-action@v1
@@ -76,12 +76,10 @@ jobs:
         with:
           version: '1'
       - uses: julia-actions/cache@v1
-      - run: |
-          julia --project=test/themes/ -e '
-            using Pkg
-            Pkg.instantiate()
-            Pkg.develop(PackageSpec(path=pwd()))'
-      - run: julia --project=test/themes test/themes/themes.jl
+      - name: Install dependencies
+        run: julia --color=yes --project=test/themes/ docs/instantiate.jl test/themes/
+      - name: Verify theme CSS files
+        run: julia --project=test/themes test/themes/themes.jl
 
   prerender:
     name: "NodeJS for prerender"
@@ -118,12 +116,10 @@ jobs:
         with:
           version: '1'
       - uses: julia-actions/cache@v1
-      - run: |
-          julia --color=yes --project=docs/ -e '
-            using Pkg
-            Pkg.develop(PackageSpec(path=pwd()))
-            Pkg.instantiate()'
-      - run: julia --color=yes --project=docs/ docs/make.jl ${{ matrix.format }}
+      - name: Install dependencies
+        run: julia --color=yes --project=docs/ docs/instantiate.jl
+      - name: Build the manual
+        run: julia --color=yes --project=docs/ docs/make.jl ${{ matrix.format }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }}
@@ -154,7 +150,7 @@ jobs:
         with:
           version: '1.6'
       - name: Install dependencies
-        run: julia --color=yes --project=docs/ -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.instantiate()'
+        run: julia --color=yes --project=docs/ docs/instantiate.jl
       - name: Build and check documentation
         run: julia --color=yes --project=docs/ docs/make.jl linkcheck
 
diff --git a/.gitignore b/.gitignore
index e2a525adc8..8818dc77e3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,7 +10,9 @@ test/missingdocs/build/
 test/nongit/build/
 test/errors/build/
 test/prerender/build/
+test/themes/dev/
 test/workdir/builds/
+docs/dev/
 docs/build/
 docs/build-pdf/
 docs/site/
diff --git a/Project.toml b/Project.toml
index accf3c11a4..3aa2757059 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "Documenter"
 uuid = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
-version = "0.27.18"
+version = "0.28.0-DEV"
 
 [deps]
 ANSIColoredPrinters = "a4c015fc-c6ff-483c-b24f-f7ea428134e9"
diff --git a/docs/Project.toml b/docs/Project.toml
index 970e018f00..2742e84b27 100644
--- a/docs/Project.toml
+++ b/docs/Project.toml
@@ -1,6 +1,3 @@
 [deps]
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 DocumenterTools = "35a29f4d-8980-5a13-9543-d66fff28ecb8"
-
-[compat]
-DocumenterTools = "=0.1.14"
diff --git a/docs/instantiate.jl b/docs/instantiate.jl
new file mode 100644
index 0000000000..e440e3e855
--- /dev/null
+++ b/docs/instantiate.jl
@@ -0,0 +1,22 @@
+# This script can be used to quickly instantiate the docs/Project.toml enviroment.
+using Pkg
+documenter_directory = joinpath(@__DIR__, "..")
+project_directory = isempty(ARGS) ? @__DIR__() : joinpath(pwd(), ARGS[1])
+cd(project_directory) do
+    Pkg.activate(project_directory)
+    # Install a DocumenterTools version that declares compatibility with Documenter 0.28,
+    # but from an unreleased tag.
+    # https://github.com/JuliaDocs/DocumenterTools.jl/releases/tag/documenter-v0.1.14%2B0.28.0-DEV
+    if isdir("dev/DocumenterTools")
+        @info "DocumenterTools already cloned to dev/DocumenterTools"
+        run(`git -C dev/DocumenterTools fetch origin`)
+    else
+        run(`git clone -n https://github.com/JuliaDocs/DocumenterTools.jl.git dev/DocumenterTools`)
+    end
+    run(`git -C dev/DocumenterTools checkout documenter-v0.1.14+0.28.0-DEV`)
+    Pkg.develop([
+        PackageSpec(path = documenter_directory),
+        PackageSpec(path = "dev/DocumenterTools"),
+    ])
+    Pkg.instantiate()
+end
diff --git a/test/themes/Project.toml b/test/themes/Project.toml
index 81fd31423c..c1ea290510 100644
--- a/test/themes/Project.toml
+++ b/test/themes/Project.toml
@@ -4,5 +4,4 @@ DocumenterTools = "35a29f4d-8980-5a13-9543-d66fff28ecb8"
 libsass_jll = "47bcb7c8-5119-555a-9eeb-0afcc36cd728"
 
 [compat]
-DocumenterTools = "=0.1.12"
 libsass_jll = "~3.6"