diff --git a/delta_q/models.txt b/delta_q/models.txt
index 8ff6caf..6415527 100644
--- a/delta_q/models.txt
+++ b/delta_q/models.txt
@@ -37,4 +37,28 @@ validateEB:
 CDF[(1, 1)]
 
 validateIB:
-CDF[(3, 1)]
\ No newline at end of file
+CDF[(3, 1)]
+
+4 -- better modelling of Leios (in format for import into editor)
+
+-- diffusion of one IB (assuming 1MB)
+diffuseIB := hopIB 0.6<>99.4 ((hopIB ->- hopIB) 8.58<>90.82 (((hopIB ->- hopIB) ->- hopIB) 65.86<>24.96 (((hopIB ->- hopIB) ->- hopIB) ->- hopIB)))
+-- diffusion of one EB (assuming 64kB)
+diffuseEB := hopEB 0.6<>99.4 ((hopEB ->- hopEB) 8.58<>90.82 (((hopEB ->- hopEB) ->- hopEB) 65.86<>24.96 (((hopEB ->- hopEB) ->- hopEB) ->- hopEB)))
+
+-- single link latencies across continents
+far := CDF[(0.268, 1)]
+farL := CDF[(0.531, 1)]
+farXL := CDF[(1.598, 1)]
+-- single link latencies between data centers within a continent
+mid := CDF[(0.069, 1)]
+midL := CDF[(0.143, 1)]
+midXL := CDF[(0.404, 1)]
+-- single link latencies within a data center
+near := CDF[(0.012, 1)]
+nearL := CDF[(0.024, 1)]
+nearXL := CDF[(0.078, 1)]
+
+-- a hop (for an IB or EB) is a choice of near/mid/far with req-res-req-resLarge in each arm
+hopIB := (((near ->- near) ->- near) ->- nearXL) 1<>2 ((((mid ->- mid) ->- mid) ->- midXL) 1<>1 (((far ->- far) ->- far) ->- farXL))
+hopEB := (((near ->- near) ->- near) ->- nearL) 1<>2 ((((mid ->- mid) ->- mid) ->- midL) 1<>1 (((far ->- far) ->- far) ->- farL))
diff --git a/delta_q/src/bin/editor-web.rs b/delta_q/src/bin/editor-web.rs
index 2c37601..d0716fc 100644
--- a/delta_q/src/bin/editor-web.rs
+++ b/delta_q/src/bin/editor-web.rs
@@ -5,11 +5,12 @@ macro_rules! cloned {
     }};
 }
 
-use delta_q::{CalcCdf, DeltaQ, DeltaQComponent, DeltaQContext, EvaluationContext};
+use delta_q::{CalcCdf, DeltaQ, DeltaQComponent, DeltaQContext, EvalCtxAction, EvaluationContext};
 use gloo_utils::window;
 use js_sys::Reflect;
+use std::str::FromStr;
 use wasm_bindgen::{prelude::Closure, JsCast, JsValue};
-use web_sys::{HtmlInputElement, MessageEvent, MessageEventInit};
+use web_sys::{HtmlInputElement, HtmlTextAreaElement, MessageEvent, MessageEventInit};
 use yew::{prelude::*, suspense::use_future_with};
 use yew_agent::{oneshot::OneshotProvider, prelude::use_oneshot_runner};
 use yew_hooks::use_local_storage;
@@ -22,12 +23,57 @@ fn app_main() -> HtmlResult {
         ctx_handle.set((*ctx).clone());
     }
 
-    let selected = use_state::<Option<String>, _>(|| None);
-    let select = cloned!(selected; Callback::from(move |n| selected.set(Some(n))));
-
     // epoch counter to trigger recomputation when the context changes
     let epoch = use_state(|| 0);
 
+    let ctx_popup = use_state(|| false);
+    let ctx_text = use_state(|| String::new());
+    let ctx_text_status = use_state(|| "OK".to_owned());
+    let ctx_text_ref = use_node_ref();
+
+    let ctx_text_input = Callback::from(cloned!(ctx_text, ctx_text_status; move |e: InputEvent| {
+        let text = e.target_unchecked_into::<HtmlInputElement>().value();
+        match text.parse::<EvaluationContext>() {
+            Ok(_) => ctx_text_status.set("OK".to_owned()),
+            Err(e) => ctx_text_status.set(e),
+        }
+        ctx_text.set(text);
+    }));
+    let ctx_popup_show = Callback::from(cloned!(ctx_popup, ctx_text, ctx; move |_: MouseEvent| {
+        ctx_popup.set(true);
+        ctx_text.set(ctx.to_string());
+    }));
+    use_effect_with(
+        ctx_popup.clone(),
+        cloned!(ctx_text_ref, ctx_text, ctx_popup; move |popup| {
+            if **popup {
+                let Some(textarea) = ctx_text_ref.cast::<HtmlTextAreaElement>() else {
+                    return;
+                };
+                textarea.focus().expect("focus failed");
+                textarea.set_value(&*ctx_text);
+                let escape = Closure::<dyn Fn(KeyboardEvent)>::new(move |e: KeyboardEvent| if e.key() == "Escape" {
+                    ctx_popup.set(false)
+                }).into_js_value();
+                textarea.add_event_listener_with_callback("keydown", escape.unchecked_ref()).expect("listening on keydown failed");
+            }
+        }),
+    );
+    let ctx_popup_close =
+        Callback::from(cloned!(ctx_popup, ctx_text, epoch, ctx; move |save: bool| {
+            ctx_popup.set(false);
+            if !save {
+                return;
+            }
+            if let Ok(cx) = EvaluationContext::from_str(&*ctx_text) {
+                ctx.dispatch(EvalCtxAction::Set(cx));
+                epoch.set(*epoch + 1);
+            }
+        }));
+
+    let selected = use_state::<Option<String>, _>(|| None);
+    let select = cloned!(selected; Callback::from(move |n| selected.set(Some(n))));
+
     let agent_status = use_state(|| "".to_owned());
     let agent = use_oneshot_runner::<CalcCdf>();
     use_future_with(
@@ -59,7 +105,11 @@ fn app_main() -> HtmlResult {
 
     let on_change = cloned!(ctx, epoch;
         Callback::from(move |(name, dq): (String, Option<DeltaQ>)| {
-            ctx.dispatch((name.clone(), dq.clone()));
+            if let Some(dq) = dq {
+                ctx.dispatch(EvalCtxAction::Put(name.clone(), dq));
+            } else {
+                ctx.dispatch(EvalCtxAction::Remove(name));
+            }
             epoch.set(*epoch + 1);
         })
     );
@@ -101,7 +151,7 @@ fn app_main() -> HtmlResult {
 
     Ok(html! {
     <div>
-        <p>{ "context:" }</p>
+        <p>{ "context:" }<button onclick={ctx_popup_show}>{ "edit" }</button></p>
         <ul>
         { list_items }
         </ul>
@@ -115,6 +165,16 @@ fn app_main() -> HtmlResult {
             </div>
         }
         <p>{ "agent status: " }{ &*agent_status }</p>
+        if *ctx_popup {
+            <div class={classes!("ctx_popup")}>
+                <p>
+                    <button onclick={cloned!(ctx_popup_close; move |_| ctx_popup_close.emit(true))} disabled={&*ctx_text_status != "OK"} >{ "save" }</button>
+                    <button onclick={cloned!(ctx_popup_close; move |_| ctx_popup_close.emit(false))} >{ "cancel" }</button>
+                </p>
+                <textarea oninput={ctx_text_input} rows={(ctx_text.lines().count() + 1).to_string()} cols="80" ref={ctx_text_ref} />
+                <pre>{ &*ctx_text_status }</pre>
+            </div>
+        }
     </div>
     })
 }
@@ -157,6 +217,7 @@ struct EditExpressionProps {
 #[function_component(EditExpression)]
 fn edit_expression(props: &EditExpressionProps) -> HtmlResult {
     let name = props.name.clone();
+    let orig = props.value.clone();
     let on_change = props.on_change.clone();
 
     let editing = use_state(|| false);
@@ -196,14 +257,17 @@ fn edit_expression(props: &EditExpressionProps) -> HtmlResult {
     let field = use_node_ref();
     use_effect_with(
         editing.clone(),
-        cloned!(field; move |editing| {
+        cloned!(field, buffer; move |editing| {
             if **editing {
                 let Some(field) = field.cast::<HtmlInputElement>() else {
                     return;
                 };
                 field.focus().expect("focus failed");
-                let escape = Closure::<dyn Fn()>::new(cloned!(editing; move || editing.set(false))).into_js_value();
+                let escape = Closure::<dyn Fn(KeyboardEvent)>::new(cloned!(editing; move |e: KeyboardEvent| if e.key() == "Escape" {
+                    editing.set(false)
+                })).into_js_value();
                 field.add_event_listener_with_callback("keydown", escape.unchecked_ref()).expect("listening on keydown failed");
+                buffer.set(orig.to_string());
             }
         }),
     );
diff --git a/delta_q/src/delta_q.rs b/delta_q/src/delta_q.rs
index 9f5f340..2a38607 100644
--- a/delta_q/src/delta_q.rs
+++ b/delta_q/src/delta_q.rs
@@ -1,4 +1,4 @@
-use crate::{cdf::DEFAULT_MAX_SIZE, CDFError, CompactionMode, CDF};
+use crate::{cdf::DEFAULT_MAX_SIZE, parser::eval_ctx, CDFError, CompactionMode, CDF};
 use smallstr::SmallString;
 use std::{
     collections::{BTreeMap, BTreeSet},
@@ -46,6 +46,14 @@ pub struct EvaluationContext {
     mode: CompactionMode,
 }
 
+impl FromStr for EvaluationContext {
+    type Err = String;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        eval_ctx(s)
+    }
+}
+
 impl Default for EvaluationContext {
     fn default() -> Self {
         Self {
diff --git a/delta_q/src/lib.rs b/delta_q/src/lib.rs
index d2fea52..d7701c9 100644
--- a/delta_q/src/lib.rs
+++ b/delta_q/src/lib.rs
@@ -15,4 +15,4 @@ mod render;
 pub use agent::CalcCdf;
 pub use cdf::{CDFError, CompactionMode, CDF};
 pub use delta_q::{DeltaQ, EvaluationContext};
-pub use render::{DeltaQComponent, DeltaQContext};
+pub use render::{DeltaQComponent, DeltaQContext, EvalCtxAction};
diff --git a/delta_q/src/render.rs b/delta_q/src/render.rs
index a9fd9b3..e9c038a 100644
--- a/delta_q/src/render.rs
+++ b/delta_q/src/render.rs
@@ -453,16 +453,28 @@ fn branch(props: &BranchProps) -> Html {
     }
 }
 
+pub enum EvalCtxAction {
+    Put(String, DeltaQ),
+    Remove(String),
+    Set(EvaluationContext),
+}
+
 impl Reducible for EvaluationContext {
-    type Action = (String, Option<DeltaQ>);
-
-    fn reduce(self: Rc<Self>, (name, dq): Self::Action) -> Rc<Self> {
-        let mut ctx = (*self).clone();
-        if let Some(dq) = dq {
-            ctx.put(name, dq);
-        } else {
-            ctx.remove(&name);
+    type Action = EvalCtxAction;
+
+    fn reduce(self: Rc<Self>, act: Self::Action) -> Rc<Self> {
+        match act {
+            EvalCtxAction::Put(name, delta_q) => {
+                let mut ret = (*self).clone();
+                ret.put(name, delta_q);
+                Rc::new(ret)
+            }
+            EvalCtxAction::Remove(name) => {
+                let mut ret = (*self).clone();
+                ret.remove(&name);
+                Rc::new(ret)
+            }
+            EvalCtxAction::Set(evaluation_context) => Rc::new(evaluation_context),
         }
-        Rc::new(ctx)
     }
 }
diff --git a/delta_q/styles.css b/delta_q/styles.css
index 6765981..863e6c3 100644
--- a/delta_q/styles.css
+++ b/delta_q/styles.css
@@ -29,6 +29,8 @@
 .dq_edit input[type="text"] { width: 100%; }
 .dq_show { margin-left: 16px; }
 .result { max-height: 5em; overflow-y: scroll; }
+.ctx_popup { z-index: 1; position: absolute; left: 20px; top: 20px; right: 20px; bottom: 20px; border: 1px solid black; background-color: lightgrey; }
+.ctx_popup textarea { width: 100%; white-space: nowrap; }
 
 .column { display: flex; flex-direction: column; }
 .row { display: flex; flex-direction: row; }